INDUSTRIAL A N D ENGINEERING CHEhlISTRY
666
Free chlorine and the fumes of bleaching powder are so corrosive that a paint that will withstand sulfuric acid will not withstand chlorine products-in fact, in many instances it is advisable, where rust pittings are very bad, t o paint the steel with a waterproof paint and then put on a 1-in. coat of portland cement grout, which of itself must be exceedingly dense, and which should then be followed with an alkaliproof, acid-proof, or chlorine-proof paint, as the case may be. WOOD
Wooden vats present a very important problem in painting. Some years ago i t was the general impression that a wooden vat, whether connected with a sprinkler system on the roof of a building or used in the interior of a building, needed no coating, but looking out over the sky line of the City of New York, where practically every big building is sprinklered, and therefore has a 5000 or 10,000-gal. tank from 10 to 20 ft. above the roof, you seldom see one that has not been painted on the outside, and even if you do see one that is unpainted, the hoops are always painted. There is a simple problem in engineering which regulates why a vat should be unpainted on the inside and painted on the outside-one of tension and compression. From the writer’s experience-and his firm has over 100 wooden tanks in its factory-he has found that continual painting and continual looking after the hoops save the price of many a new tank. I n alcoholic fermentation, when beer was manufactured in this country, it was found that the only material which was suitable for the painting of the interior of wooden fermentation tanks was a mixture of practically pure, acetone-free ethyl alcohol and 4 lbs. of the highest grade of East India shellac, known as “DC” or as “VSO,” and because only between 3 and 5 per cent of alcohol was generated, the coating was not affected and withstood the action of the mash for about six months. It was subsequently found, however, that this mixture, which was known throughout the trade as ‘(brewers’varnish,” was expensive to apply, and a great many objected to it on account of the alcoholic fumes. Since then a much better material has been placed on the market, which is in the form of a wax. It is unaffected by acids, alkalies, or alcohols, and is harmless to the workman who applies it, because it contains no volatile matter. This appears to be a very high grade of resin copal, similar t o kauri, which has been melted with some form of wax, and when this material is applied with a blow torch and thoroughly impregnated into the interior of the tank, it has been known to last for four or five years. Chemical manufacturers have adopted materials of this type for the interior of vats, and experiments show that both strong vinegar and hydrochloric acid have no effect on a coating of this type.
BRICKAND HOLLOW TILE Brick and hollow tile should either be painted or should have a colorless application where the original texture is to be preserved. In the last few years we have made so many advances in the treatment of tung oil that these colorless coatings are to be had in endless varieties. A camera which occupies two rooms of the Department of the Interior building is now used for photographing maps of the United States, maps of oil fields, and charts showing mineral resources. The lens, bellows, and copy-holder are in one room, and the plate-holder and dark room are in the other room. The camera will take a picture one yard square It weighs 7000 lbs. and is operated either by hand or by electricity. Focusing IS done by means of a n electrical contrivance.
Vol. 15, No.?
The Resistivity of Various Materials towards Photographic Solutions’ By J. I. Crabtree and Glenn E. Matthews EASTMAN KODAK Co., ROCHESTER, N. Y.
A
LTHOUGH much information is available in the litera-
ture concerning the effect of alkalies, acids, and numerous other solutions on materials which might be suitable for constructing trays, tanks, film holders, etc., for photographic purposes,1s21*very little of this information throws any light on the probable effect of photographic solutions on these materials. The suitability of a material from a photographic standpoint depends on two factors-namely, the resistivity of the material to the action of the photographic solution, and the effect of the material on the useful life of the solution. The second factor is of great importance, since a solution such as a developer may appear unchanged after a week’s exposure to a metal, but on testing the developer may be found to fog emulsions badly. In. this event the metal would be,entirely unsuitable for constructing developing apparatus, but i t might be satisfactory for fixing, washing, or toning apparatus. A material which is resistant and does not produce undesirable effects with any photographic solution is, of course, t o be preferred. Of the possible materials suitable for constructing photographic apparatus, the following were considered: 1-Metals, plated metals, and alloys 2-Nonmetallic materials: Enameled steel Glass Impregnated fibrous materials Lacquered metal Porcelain and glazed earthenware Rubber, rubber composition, and nitrocellulose materials Slate and alberene stone Wood
METALS,PLATED METALS,AND ALLOYS The ductility of metals and alloys and the fact that they can be readily soldered and welded would seem to render them particularly, suitable for the manufacture of photographic apparatus; although to date no satisfactory metal or alloy is known which is entirely suitable for use with all photographic solutions, it is necessary to restrict their use to specific purposes. Fixing baths are the most corrosive on account of their frequently high acidity, and in a used bath, if any metal less noble than silver is immersed therein, silver is deposited on the metal and an equivalent quantity of the metal goes into solution. Such a coating of silver usually renders the metal more resistant, though if the under layer of metal is exposed to an acid solution free from silver, electrolytic corrosion sets in. Pure silver is satisfactory except for toning solutions. Lead has been extensively used for lining wooden tanks and trays, and has proved satisfactory except for some toning solutions, while lead-coated stee13j4 offers promise. Zinc has been used for washing tanks and is fairly satisfactory for this purpose. Pure tin has long been employed for conveying distilled water. Nickel-plated brass is satisfactory for small developing tanks when they are used intermittently, but plated metals invariably corrode in contact with fixing solutions. Thus, a nickel-plated copper rack for holding photographic plates fell to piece^.^ 1 Communication No. 176 from the Research Laboratory of the Eastman Kodak Company. Numbers in the text refer to the bibliography a t the end of the article.
*
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
J d y , 1923
Discolored solutions are often produced by a reaction between the metal and the developing or fixing solution, and in time stain the gelatin film. Thus, iron forms purple stains with a pyro d e ~ e l o p e r . ~ Although numerous alloys have appeared during the past few Monel metal is the only one which has been adopted to any extent for photographic use, and this alloy is not entirely resistant t o acid fixing solutions. I n order to obtain data as to the relative resistivity of various metals, plated metals, and alloys, the following were examined : MNTALS Aluminium Copper Iron Lead Nickel Tin (block) Zinc
PLATED METALS Galvanized iron Tinned iron
ALLOYS Aterite No. 136 (Cu-Ni-Zn) Brass (commercial sheet) Duriron Monel Niaco (Ni alloy) Nickel Silver (Cu-Ni-Zn-Fe) Nicolene (Ni-Cu) Phosphor bronze (Cu-Sn-P) Solder A (80 Pb-20% Sn) Solder B (20% Pb-80% Sn) Rezistal steel (Cr steel) Type metal (Ph-Sb)
These metals and alloys were tested with the following photographic chemicals: 1-Developers. (NOTE: The formulas are expressed in abbreviated form-namely, the number of grams of egch constituent in the following in a liter of solution ready to use-arranged order: reducing agent, sodium carbonate (dry); sodium sulfite (dry) ; potassium bromide.) (a) Elon-hydroquinone zr:o$ :none 9.2-48-96-2 (low elon content) Elon 4.0 ( 6 ) Elon-hydroquinone Hydroquinone 1.0-20-1 0 4 . 5 (high elon content) Sodium bisulfite 10 Pyro 10-37. $35-0.5 (G) Pyro (two solution) Sodium bisulfite 8.5 2-Fixing Baths.
.(
i
30 per cent hypo solution ( b ) Arid hypo solution (formula in grams per liter) (a)
Hypo 300
Sodium sulfite 4.5
28 per cent acetic acid 25 cc.
Potassiua alum 3.0
(c)
Partially exhausted acid hypo solution ( b ) containing dissolved silver ( d ) Completely exhausted acid hypo solution ( b ) containing dissolved silver 3-A hypo-alum Toning Bath, containing potassium alum, hypo, silver nitrate, and sodium chloride. 4-Water. Information as to the effect of moisture on the materials was desired in order t o detmmine the most suitable metal or alloy for constructing washing and rinsing tanks. 5-Dilute Acids. The photographer often has occasion t o use solutions of dilute acids, and a number of the metals and alloys were tested to determine their relative resistance to dilute nitric and sulfuric acids.
EXPERIMESTAL D E T - ~ I L S - ~ of ~ ~metal, ~ ~ S 2 x 4 in. and approximately 20 gage in thickness, were placed in 260-cc. Pyrex beakers containing 200 cc. of solution. Usually, duplicate sets were made up, keeping one set at room temperature, 65" to 70" F., and the other at a tropical temperature, 110" to 120" F. Examination was made at the end of 24 or 48 hrs., 1 wk., 2 wks., and if the test was of sufficient interest it was continued for a longer period. The volume was kept constant by adding water a t regular intervals. I n each case, the following observations were made: 1-Appearance of the Solution. I n the case of developers, the fog, which was produced on motion picture positive film after 15 min., was measured by means of the usual type of densitometer. 2:Efect o n the Metal. Inspection was made with the aid of a microscope.
EFFECT OF DEVELOPERS-In general, it was found that metals or alloys containing either copper or tin produce excessive fog with developers. From this standpoint, the following are unsatisfactory: copper, tin, tinned iron, brass,
667
phosphor bronze, and Solders A and B. Several of etals and alloys, especially aluminium, iron, gal iron, Duriron, and Rezistal steel, were not visibly and the developer in which they were immersed did no2 produce fog, but the solutions were badly discolored and would no doubt stain emulsions. Of the remaining m e t d i e materials, the most satisfactory were lead, nickel, Aterite No. 136, Kiaco, Nicolene, nickel silver, Monel, and type metal. The developer solutions in which these metals had been immersed were not objectionably changed in appearance, did not fog, and exhibited only a slight corrosive action on the metals. The results obtained with the first elon-hydroquinone developer (a) after one day and at the end of a week a t a temperature of 110' F. are given in Table I. Tests made with Developers b and c confirmed these results. TABLEI-EI.ON-HYDROQTJINONEDEVELOPER US. METALSAND ALLOYS (Temperature, llOo t o 120° F.) A bbreuiations: Condition of Solution. D, darker than blank: I,, lighter t h a n blank: MD, much darker than blank NC, no change; P p t , precipitate. Condition of Metal. C , cdrroded; Dp, deposit on surface; E, etched; S, stained; U, unchanged. ,----- 24 HRS.--------ONE WEEK----Condition ofFog --Condition of--- Fog METALS Solution Metal Density Solution Metal Density 0.76 Tin Ppt. U 1.26 Ppt. I3 Copper NC D-Ppt. E 0.50 E-C 0 . 4 1 Aluminium D-Ppt. D-Ppt. 0.09 Dp-E 0.23 DP Zinc D D 0.14 E Dp 0.22 0.14 Nickel NC U 0.20 NC u D D 0.10 IJ 0.19 Lead u D 0.18 MD-Ppt. Iron IJ U 0.14
PLATED METALS Tinned iron NC Galvanized iron NC ALLOYS Solder R NC Solder A NC Brass D Phosphor bronze D Rezistal steel NC Type metal L Duriron NC Aterite No. 136 I. Nickel silver L Nicolene L Niaco NC Monel NC B!ank Clear amber color
:
E
0.70 0.18
E
L-Ppt. 2 50 E 2 50 L-Ppt. E 0 30 D-Ppt. DP D S 0 41 D-Ppt. u 0 33 I3 034 L 11 031 D S 0 22 I, S 026 L 0 28 L u 7J 022 D 0 20 Ppt. 0 26 Clear deep straw Slight ppt.
S-E U Dp S-Dp U
E
U
s S
KJ U U
I,-Ppt. D
v
0.24 0.14 1.60 1.40 0.45 0.38 0.26 0.24 0.28 0.16 0.24' 0.20 0.20 0.12 0.18
ADDITIONO F METALLIC SALTS TO DEa corroborative parallel to the work carried out with developers and metals and alloys, the effect of adding the following metallic salts to the developer was studied: A12Cls.12Hz0; CuC12; FeCI3; NiC12; Pb(C2H302)Z; SnC12; SnCI4; ZnC12; and Zn(C&H302)2.Two sets of experiments were conducted using Developer a. I n the first group of experiments the salts were added so as to give concentrations of 0.1 g. per liter of developer, and in the second group, 1.0 g. per liter. The results checked very well with those found with the actual metals and alloys. Of the salts examined, only copper and stannous tin produced fog, the latter exhibiting the most fogging action, even producing fog slightly above that of the blank in concentrations as low as 0.01 g. per liter. The fogging action of traces of copper or stannous salts is especially noticeable when developing film on a reel. The precise action of a copper salt in causing fog is not thoroughly understood-presumably it acts as a catalyst in accelerating the rate of oxidation of the developer, and it is well known that developer oxidation products cause fog. Stannous salts reduce the unexposed silver grains of the emulsion t o metallic silver, which constitutes the fog. EFFECTOF METALLICCOUPLESON THE RATE OF CORROSION-In the course of a series of testg on metal tanks of a copper-nickel alloy, X, soldered on the inside with lead-tin solder, it was observed that if a developing solution remained in the tank for ,z short time the developer gave very bad fog. The cause of this excessive fogging action was traced to the EFFECTOF
VELOPERS-&
THE
presence of tin in the developer, which w nto solution. It was obt oxidize as rapidly as a a glass tank, which w in the.&annons condition, m aerial oxidation, (The keeping qualities of a developer was observed by Desalme,*) As a result of this observation, tests were made to determine if electrolysis A strip of Alloy tent) were placed in a being insulated from e wjth the metals connected externally by means of a copper wire. A further test was made with Solder B (high tin content). Fog tests were made with, the developers a t periodic intervals, and i t was found that if the metals were not in metallic connection within a week the developer gave only a slightly increased iog, whereas if the metals were externally connected the developer gave very bad fog. The fog measurements were as follows:
Solder A-Alloy X Solder B-Alloy X Blank
Vol. 15, N6. 7
I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
668
-4 Hrs.-C U 3 00 0 74 2 29 0.75 0 20
F ~ DGE ~ S I T Y 7 - 2 4 Hrs --48 C U C
--.
1 78 1 97 C = U =
0 66 0.31
0 04 Connected Unconnected
Hrs.-U
1 77 0 51 2 12 0 25 0.04
The falling off in the fogging action with time was attributed to the oxidation of the stannous salt to the stannic condition. Fuller experimental details will be given in a future paper on the effect of electrolysis on the rate of corrosion of metals in photographic solutions. , The practical application of these .experiments is as follows: Tin and copper or alloys containing these metals should not be used in metallic contact with a more noble metal in the presence of developing or fixing solutions. For instance, a lkad-lined tank should not be soldered, but should be leadis, the burned, and the same applies to lead piping-that joints should be "wiped" and not soldered. I n the case of the metal tanks above where the joints were soldered on the outside, no developer fog was produced. EFFECTOF FIXIKG BATHS-An acid fixing bath is very corrosive, and as far as is known no metal or alloy has yet been found which under all conditions is resistant to fixing baths. The metal or alloy to be satisfactory should withstand the following tests: 1-It should be free from corrosion after two weeks' contact under tropical conditions with either fresh or exhausted fixing baths. %-It should not produce undesirable changes in the appearance of the bath, such as ( a ) precipitation of dissolved constituents, ( h ) formation of foam or scum a t the surface of the solution, or ( c ) objectional discoloration of the bath.
Any loss in the ratexof fixation which was caused by any of these effects would be sufficient reason for rejection of the the material. Tests made with the four different fixing baths previously described may be summarized as follows: 1-Lead, nickel, Niaco, monel, type metal, and Rezistal steel are fairly satisfactory. With lead, nickel, brass, and Monel in partially and completely exhausted fixing baths, a layer of silver plates out of the solution on the metals. 2--Copper, iron, tin, tinned iron, Duriron, nickel silver, phosphor bronze, and Solders A and B are attacked t o a varying extent. They discolor the bath, and enough precipitation occurs t o cause them to be undesirable. 3-Aluminium, zinc, galvanized iron, Aterite No. 136, and Nicolene are very unsatisfactory. All corrode badly, the fixing baths are covered with a thick scum, and heavy precipitates are formed. (The effect of electrolysis on the rate of corrosion of metals and alloys in fixing baths will be dealt with in a future paper.)
The results obtained with a partially exhausted bath (c) and comparable with those found with the other fixing baths are given in Table 11. ABLE II-PARTIAI,LY EXHAUSTED FIXING BATHvs. METALSAND BLLOYS A bbwviations: Condition of solution. NC, no change; F, foam on surface; Ppt., precipitate: H. ppt., heavy piecipitste. D darker than blank. Condition of metal: RC, badly dorrdhed; C,'corroded; Dp, deposit on surface; E, etched; I n , incrustation. SE, slightly etched, S , qtained. = Test made a t room temperature. -24 HRS.------ONE WEEK----Condition of----Condition of----. Solution Metal Solution Metal Room Temperalure (68' F . ) METALS Aluminium E D-F-H. Ppt. C-Dp F-Ppt. of Ag F - p p t . of C ' Zinc D-F-Ppt. C-Dp
(s) -
---
-
.
*
-w
Iron Tin Copper Lead Nickel
Blackppt. White ppt. Black ppt. Slight ppt. NC
PLATED METALS Galvanized F-D-I€. iron ppt. of Ag Tinned iron NC
DP
Dp Dp Dp
D-Ppt. H. ppt. Gray D (blue)-Ppt. Ppt. Ppt.
Pasty D p SE-Dp Thick Dp Thin D p DP
C
Thick F-H. Ppt.
BC-B!ack DP Brown-Dp
S-SE
Dp
Ppt. Troptcal Temperature (110' F . )
ALLOYS Nicolene
F-D-H. C-Dp ppt. Ag Aterite No. 136 Ppt. E-Polish gone Nickel silver NC White D p
Solder A
Thin Ag plating Brown DpH. ppt. Ag plating Black D p D Dp-In Light ppt. Ppt.
Solder B
-
Duriron Phosphor bronze (R) Type metal'
(E)
D-ppt. NC D-Ppt.
Niaco
Pale White Dp green PS'C ThinDp Light yellow PPt. of sulfur
(g)
H . ppt. Black
BC-Dp Ag plated BC-Dp
Light green ppt.
SE - Rough
H. ppt.
Dlatinr Arblistered Black D p
H. ppt. D-ppt. Ppt.
Brown Dp- H. ppt. Ae Dlatinn b&w DpDP NC S-Ag plate rMilky black PPt.
Brass Rezistal steel
Monel Blank
Black ppt. Ag
Ppt.
SE+Black DP Black D p Black Dp S-Dp Black Dp D p - Rust near surface Black Dp-
NC DP Light yellow Slightly heavier PPt.
SE
EFFECTOF HYPO-ALUMTONING BATH-AImost all the metals and alloys tested exhibited a vigorous and undesirable reaction with the hypo-alum toning bath. The experiments were conducted for one week a t a temperature of 110" t o 120" F., or approximately a t the temperature a t which the bath is recommended for use. The reaction was evidenced by corrosion of the metal, a darkening of the precipitated sulfur in the solution, and the deposition of colored oxides and sulfides on the surface of the metals and the container. Lead, nickel, and Monel were least affected, but even these metals are not entirely satisfactory with toning baths. Aluminium, copper, zinc, brass, phosphor bronze, and galvanized iron showed visible corrosion. These experiments confirm the experience of Crabtree and B ~ l l o c k ,that ~ "a hypo-alum bath in contact with pure lead for one week is slower in action and produces stains, especially on the back of prints. I n general, a metal which combines a t all readily with nascent sulfur or which displaces silver from its thiosulfate is not suitable as a container for hypoalum toning baths." For toning solutions, glass, porcelain, or enameled apparatus are to be recommended rather than metallic containers. The results found with the hypo-alum toning bath over one week at a temperature of 110" to 120" F. are indicated in Table 111. EFFECT O F WATEROR MOISTURE-After exposure to t a p water for one week a t 100" to 120" F., the following metals were slightly corroded and the water in which they were immersed was filled with varying quantities of precipitates: aluminium, iron, zinc, galvanized iron, and tinned iron. Iron
INDUSTRIAL A N D EhTGINEERING CHEMISTRY
Ju?y, 1923
TABLE111-HYPO-ALUM TONINGBATH DS. METALSAND ALLOYS (Temperature 110' F.) Abbreviations: Condition of solution: D , darker than blank; H. Ppt., heavy precipitate: L, lighter than blahk; "2, no change; Ppt., precipitate; Soln., solution. Condition of metal: BC, badly corroded; C, corroded; Dp, deposit; E, etched; In, incrustation; S, stained; T. Dp., thick deposit. ----24 HRS.---ONE WEEK-----Condition of------Condition of-METALS Solution Metal Solution Metal BC-Dp H. Ppt. Aluminium D-H. Ppt. C-In C H. Ppt.-Soh. BC-Dp Zinc Ppt. pale pink (pink) D-Ppt. Black In D-H. Ppt. T. Dp. Copper (crystalline) Iron D-Ppt. Gray D p H. Ppt. DP (red) D-Ppt. Black D p D-H. Ppt. Grey Dp Lead Thin Dp Nickel NC Soln. pale green Dp
----
PLATED METALS Gtlvanized D-Ppt. iron Tinned iron Brown PPt. ALLOYS Phosphor bronze Brass Monel Blank
C-Zn coat- L-Ppt. ing removed Brown Dp. Soln. yellow H. Ppt.
D-Ppt.
Powdery DP. D-Ppt. S-Dp. D Thin Dp. Partlv lilted with ppt. of sulfur
BC-T. Dp. DP b e l low)
Black Ppt.
C-T. Dp.
D-H. P p t . S o h . pale green Soln. darker gray PPt.
E-T. Dp.
Black D p
and tinned iron were the most corroded. Copper, lead, nickel, Monel, and phosphor bronze were unchanged. EFFECT OF DILUTE AcIDs-Several of the metals and alloys were tested with solutions of 5 per cent nitric acid and with 5 per cent sulfuric acid for one week a t 110" to 120" F. The strips were examined after 24 hrs. and a t the end of the week. As a rough indication of the relative attack of the two acids, the metal strips were weighed before and after the tests. The results, computed on the basis of the loss in grams per 100 sq. in. of immersed surface per day, are given in Table IV. TABLE IV-EFFECT
OF DILUTEACIDS O N SEVERAL METALSA N D ALLOYS (Results indicated as the loss in grams per 100 s q . in. per day) 5 Per cent NitFic Acid 5 Per cent Sulfuric Acid Lead Iron 10.3 11.4 Tin (block) Galvanized iron 9.4 10.9 Galvanized iron 5.8 Zinc 8.9 Nickel 3.1 Copper 1.1 Zinc Aluminium 2.9 0.89 Brass 2.7 Phosphor bronze 0.69 Iron 2.2 Nickel 0.69 Tin (block) Copper 1.8 0.69 Monel Phosphor bronze 1.1 0.69 Monel Brass 0.45 0.22 Aluminium 0.22 Lead None
I n general, the metals and alloys were attacked more strongly by 5 per cent nitric acid than by 5 per cent sulfuric acid. Aluminium, phosphor bronze, and Monel were least affected by both acids. Lead was very badly corroded by dilute nitric, but gave no loss in weight with dilute sulfuric. Sickel was corroded by nitric, but was only slightly etched by sulfuric. Galvanized iron and iron were badly corroded by each acid. On the whole, Monel metal was least attacked. T\TONMETALLIC
MATERIsLS
ENAMELED STEEL-Enameled steel, or so-called glasscoated steel, is extensively used for constructing small trays and tanks, and has proved fairly satisfactory, although the vitreous coating is relatively brittle, and readily chips away if roughly handled. When the undercoating of steel is thus laid bare, i t corrodes very rapidly and the vessel is rendered useless. The coating of enamel is resistant to weak acids used in photographic practice, but with developers and alkaline solutions the surface of the coating becomes etched and roughened. It is then difficult to clean and will be permanently discolored by solutions of dyes. Enameled steel is very satisfactory for constructing small developing and fixing tanks. If the tanks are thickly coated and are not moved about, the tendency for the enamel to chip is reduced to a minimum.
669
GLASS-This is undoubtedly the most satisfactory material known to-day, but owing to its fragility it is not satisfactory for large tanks or trays. Glass apparatus should be well annealed, free from ribs, and the corners of trays and tanks rounded off so as to facilitate cleaning. For containing strong alkalies, resistive glass such as Pyrex should be used.1° IMPREGNATED FIBROUS MATERIALS-such materials consist of paper, wood, canvas, etc., impregnated with varnish, wax, shellac, or phenol condensation products (Rakelite, etc.). The impregnation is usually carried out by heating in vacuo, and then injecting wax or varnish under pressure. Trays or tanks prepared from impregnated paper or other fibrous material develop cracks with use, thus permitting access of the solutions €0 the under layers which are less completely protected. Such trays and tanks are entirely unsatisfactory for use with solutions containing strong alkalies or for fixing baths which are a p t t o disintegrate the fibrous material through crystallization as explained under "Porcelain and Glazed Earthenware." Wood impregnated with paraffin wax is very satisfactory except in hot weather when the wax is liable to s0ften.l' ,4n ingenious method of protecting metal ware such as tanks or troughs consists of first coating the surface of the metal with cloth or canvas, using glue as an adhesive, then brushing over with molten paraffin wax (high melting point), and finally smoothing off the surface with a hot iron. If the tank is rigid such a coating will withstand alkali or acid bleaching solutions, such as acid permanganate. LACQUEREDMETAL-The commonest and most satisfactory photographic lacquer consists of asphalt or a mixture of asphalt with rubber cement, the latter serving to overcome the slight brittleness of the asphalt coating. Baked japan is very satisfactory, but none of these materials will resist developing solutions containing a high percentage of alkali. Freshly applied asphalt will often produce a scum on the surface of a developer. PORCELAIN AND GLAZED EARTHENWARE-hfany varieties of these materials exist, ranging from white china ware to glazed tile material. White porcelain is usually unsatisfactory, because the glaze invariably cracks, forming minute fissures into which hypo solution penetrates, and on drying the crystallization of the hypo or other chemicals expands the fissures, causing disintegration in a manner similar to that of ice in the weathering of rocks. This is especially true in the case of open hypo tanks, when the soIution creeps up the sides of the tank, and it applies also to all biscuit ware, which is incompletely glazed or if the glaze is cracked. Tanks are now available of dark brown earthenware glazed on both sides, which are entirely satisfactory for containing photographic solutions, except very strong alkalies. They are especially recommended for storing ordinary developing and hypo solutions. RUBBER, RUBBERCOMPOSITION, AND SITROCELLULO MATERIALS-Hard rubber will withstand practically all photographic aqueous solutions a t normal temperatures, except oxidizing solutions. Hard-rubber tanks are somewhat brittle, tend to buckle out of shape in hot weather, and are comparatively expensive. Nitrocellulose is open to practically the same objections. Rubber compositions usually consist of siliceous earth mixed with pitch, asphalt, or crude oil wax, molded under heat and pressure. Such materials are relatively brittle, warp under heat, and when used as containers for salt solutions they disintegrate in the same manner as porous earthenware. The tendency for this disintegration to occur is much less if a n excess of binder is used so that the tanks or trays have a smooth surface. If the material has a rough surface or becomes etched, the crystals obtain a better grip on the walls and more strain is
I N D U S T R I A L A N D ENGINEERING CHE.WISTRY
670
exerted in the process of crystallization, thus causing more rapid disintegration. Rubber sheeting and rubberized cloth is often used for coating the inside of wooden developing trays and troughs, and is very satisfactory provided the rubber is of good quality and free from ezcessive filling material. For handling long lengths of wide film (Cirkut film) a rubberized wooden tray is ideal. Since solutions used in a tray or trough are usually discarded after use, they are in contact with the rubber for ooly a relatively short time, and therefore more corrosive solutions can be used than in the case of a rubber-lined tank. Cheap rubber sheeting or tubing which contains excessive filling material, antimony sulfide, and free sulfur is entirely unsuitable for use with developing solutions, because the alkali in the developer reacts with the sulfide forming thioantimoniate, which produces very bad chemical fog. Pure gum rubber is quite satisfactory. SLATEAND ALBWREKE SToNe-These materials are very suitable for constructing large tanks for containing developing solutions. Alberene stone is quite satisfactory for containing fixing solutions, but slate is apt to split along planes of cleavage as a result of crystallization, as previously described. Woou-Wood, such as cypress, is extensively used for constructing large tanks for handling roll and motion picture film. Teak is used for smaller tanks. Wood is satisfactory for developing, fixing, and washing purposes, and is cheaper than any other available material. It has the disadvantage that unless strongly braced the tanks have a ,tendency to warp, and in many localities fungous growths accumulate on the outside of the washing tanks and must be frequently removed. The insides of the tanks, especially wash tanks, have a propensity to accumulate slime. Wood also has the disadvantage that it becomes permanently discolored by solutions of dyes or other colored chemicals. Wood should not be painted, because alkaline developing solutions soften the paint and ultimately cause it to flake off. PRACTICAL
APPLICATION OF RESULTS
When selecting a material suitable for constructing any particular piece of photographic apparatus, several factors should be considered, namely: 1-The resistivity of the material to the most corrosive liquid with which it will come in contact. For instance, a well-galvanized iron tank is quite satisfactory for washing purposes, but not for containing fixing baths. A lead-lined tank is quite suitable for fixing baths but not for toning baths, because most metals are affected by such solutions. 2-The effect of the material on the photographic properties of the solution. For example, a copper tank containing a concentrated developer may show no visible corrosion after several days, but the small quantity of copper dissolved by the developer will be sufficient to produce chemical fog. 3-The time during which the solution will be in contact with the material. A japanned iron metal trough is suitable for toning baths if the solutions are removed and the trough well rinsed after use. If a developer is stored in a japanned tank, the japan will ultimately soften or peel off. ,&-The cost of the material. 5-The adaptability of the material for construction purposes. Glass, for instance, is entirely unsuitable for constructing large tanks because of its fragility and the difficulty of annealing such tanks.
Materials suitable for constructing various types of photographic apparatus are as follows: TRAYS,DISHES, AND SMALLTANKs-Since these containers are generally used for a variety of purposes, they should be resistant to all photographic solutions. Suitable materials are glass, enameled steel, hard rubber, teak wood impregnated with paraffin wax, wood coated with sheet rubber or rubberized cloth, well-glazed porcelain, or stoneware. Small tanks of Monel metal are satisfactory for washing or developing, and for fixing purposes,
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provided the bath is not allowed to remain in the tank for prolonged periods. DEEPTANKS (for motion picture work and amateur finishers)Alberene stone, slate, well-glazed stoneware, and wood (cypress) are suitable for all solutions, including toning baths. Leadlined wooden tanks are suitable for developing and fixing baths if the joints are lead-burned. One objection t o wood tanks is that they have a tendency to accumulate slime on the inside of t h e tank. I n the case of developers containing a low percentage of alkali, tanks of portland cement have proved satisfactory. TUBES FOR DEVELOPINGMACHINES-Hard rubber, lead, type metal, and Pyrex glassll have given satisfaction. Lead accumulates a deposit of silver from the fixing bath, and in time this tends to obstruct the tube and it has to be removed by scraping. TROUGHS FOR REEL DEVELOPMENT-Glazed stoneware and wood lined with sheet rubber or rubberized cloth are satisfactory for all solutions. Lead and Monel are satisfactory for developing and fixing solutions, provided the trough is emptied out after use. For acid oxidizing solutions or strong alkalies, the inside of the trough should be coated with cloth and this impregnated by applying molten hard paraffin wax with a brush, finally smoothing off the surface with a hot iron. Japanned metal ware is only satisfactory for temporary use. METALAPPARATUS (clips, film hangers, etc.)-Monel metal is the most satisfactory material known, but i t is not suitable for toning solutions. Tests made with Niaco and Rezistal steel alloys indicate that their resistivity approaches t h a t of Monel, although no prolonged tests with actual apparatus have been made. P I P I N G , PUMPS, FAUCETS, ETC.--For transporting developing and fixing solutions, lead and hard-rubber piping are satisfactory. Lead piping joints should be “wiped” or lead-burned, and not soldered. Faucets should be of hard rubber or stoneware, though Monel and type metal are satisfactory for developing and fixing solutions if continual exposure to the solution is not anticipated. Brass is not satisfactory for strongly acid fixing baths, but it is suitable with developers if the brass is first silverplated by immersing in a n exhausted fixing bath. Pumps 6f Monel and of phosphor bronze are satisfactory for developers and fixing baths if cleaned after use.
PRECAUTIONS TO BE: TAKEN WHEN SELECTI~G CONSTRUCTION MATERIALS I-Do not permit tin, copper, or alloys containing these metals t o come in contact with developing solutions, especially concentrated developers, because more or less of the tin or copper will dissolve and cause chemical fog. Electrolysis caused by contact of two different metals or alloys will hasten the rate of solution of the metal and thus increase the amount of fog obtained. Soldered joints are particularly to be avoided with developers, but if such joints are unavoidable a low-tin solder or one free from tin should be used and the joints so made t h a t a minimum of solder is exposed to the solution. 2-For fixing, toning, and acid oxidizing solutions such as acid permanganate, avoid metal whenever possible. If a metal must be used, lead is the most suitable for fixing baths, b u t electrolytic corrosion sets in if the joints are not lead-burned. rF o& -fixing baths or strong saline solutions, avoid porous materials such as incompletely glazed earthenware, impregnated fibro‘us materials, or rubber compositions, because crystallization of the salts within the pores of the materials causes disintegration in a manner similar t o t h a t of ice in weathering rocks. 4-Avoid cheap rubber tubing or other materials containing free sulfur or metallic sulfides for use with deveIoping solutions, became, as a result of the action of the alkali in the developer, soluble alkaline sulfides which cause chemical fog are formed.
ACKNOWLEDGMENT The authors are indebted to Harold A. Hartt for his valuable assistance during the course of this work. BIBLIOGRAPHY 1-Jones, “Materials of Construction Used in a Chemical Works,” Chem. Age (London), 4 (1921), 394, 416. 2-Merica, Chem. Met. Eng., 24 (1921), 291, 558, 649. 3-Maddy, “Coating Ferrous Metals with Lead,” U . S . Patent 1,379,998, C . A , 16 (1921), 327, “Plating Iron and Steel with Lead or Antimony,” Brass World, 17 (1921), 38. 4-I,everseege and Knapp, “Erosion of Lead,” J. SOL Chem I n d , 39 (1920), 147; Rawdon, et al., “Brittleness Developed in Pure Lead by Stress and Corrosion,” Chem. Met. E n g , 26 (1921), 109; Thresh, “Notes on the
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So-called Action of Water on Lead,” A n a l y s t , 46 (1921) 270, Rawdon, The utilization of materials that have become familiar “Intercrystalline Brittleness of Lead,” Bur. Standards, Scz Paper 577. through use in other fields is feature of recent chemical 5-“Thermit,” “Dark-Room Metal Ware,” Brzt J Phot , 69 (l922),412 engineering work. As evidence there can be cited the use B--Merlca, 6cIron-NickelAlloys,9~Chem M e t 24 (1921), 376, Johnson, “Nonmagnetic, Flame, Acid, and Rust Resisting Steel,” 16zd , Of Bakelite, hard rubber, stainless steel, chromium-nickel 26 ( I ~ z I )797, , Gillett, “Nonferrous Alloy Progress in 1921,” THISJOURNAL,alloys, etc. Each of these has advantages as a resistant ma14 (19221, 865 terial for certain limited purposes, and finds a corresponding 7--”Protective Metallic Coatings for Rustproofing Iron and Steel,” specific field of application. Pyrex glass, because of its reBur. Standards, Civc. SO (1919); Schuler, “The Covering of Chemical Appasistance to most acids combined with excellent thermal ratus with Metals and Acid Resisting Materials,” Chem. Z t g . , 46 (1921), 315; Watts, “Principles of Alloying to Resist Corrosion,” Trans. A m . Electvoproperties, has a wide field of industrial use with limits set by chem. SOC.,39 (1921), 253. design of parts and possibilities of manufacture. 8--Desalme, “Use of Salts of Tin for Preserving Developers,” Bull. soc. franc. Phot., 131 8 (1921), 192. ENGINEERING PROPERTIES OF PYREX 9-Crabtree and Bullock, “Correspondence,” B r i t . J . Phot., 66 (1919), 446. Before proceeding to a discussion of industrial applications, IO-Marshall, “Pyrex Glass as a Material for Chemical Plant Construcit is desirable to list briefly the various properties which have tion,” THIS JOURNAL, 16 (1923), 141. to be taken into consideration from the engineering standpoint, I1-“Coatings for Dishes,” Bvit. J . Phot., 66 (1919), 574; “White Wooden Trays and Sinks,” Camera Craft, 2s (1920), 367. Specific gravitya 2.25 Specific heata 0.20 Elasticity coefficientn 6230 kg per sq mm. Linear expansion coefficientb (19’ to 350’ C ) 0 0000032 per O C. Thermal conductivitya 0 0027 By A. E. Marshall1 Dielectric strengthb 20 kv. per 100 mil thickness Specific inductive capacity .5 75 to 5.78 3034 S T . PAULS T . , BALTIMORE, MD. Electrical resistivity (volume)c 1014 ohms HEMICAL engineering, considered from a somewhat Electrical resistivity (surface)c 10“ ohms a t 34 per cent humidity 5 X lo8 ohms a t 84 per cent hunarrow angle, is the translation of chemical manufacmidity turing processes from the small or laboratory scale to Corning Glass Works Laboratory. tonnage production in factories. Small-scale experiments General Electric Company Laboratory Bureau of Standards. are usually carried out in glass apparatus, with the result
Pyrex Glass Plant Equipment
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that corrosion troubles are not given much consideration until the chemical engineer is faced with the design of a small commercial plant incorporating the results of the laboratory work. Chemical corrosion of the materials to be used in construction immediately assumes importance, as the plant equipment cannot be a mere multiplication of the laboratory apparatus. The liter flask of the laboratory has to become a still, retort, or kettle of several hundred gallons capacity, the Liebig or spiral condenser has to be changed to a design capable of handling 50 or more gallons per hour, and 1/4-in. glass tubes used for connections have to be converted into 6- or %-in. pipes. I n each piece of equipment corrosion will enforce limits a3 to materials employed, and the final design will quite likely be a compromise of several materials, each selected with reference to corrosion conditions a t certain points. The introduction of industrial Pyrex a s a plant construction material has enabled the engineer to translate, within limits, laboratory practice directly into plant equipment, and to secure the freedom from corrosion enjoyed by the research chemist. The present limits of manufacture are not final, but are capable of some further expansion, as is indicated by the progression of sizes in the past eighteen months of development work. There is, of course, a limit to the size of Pyrex articles introduced, through structural considerations, but so far the present manufacturing possibilities have not reached the safe limits set by the engineering factors of plant design. FAMILIAR PROPERTIES OF PYREX Pyrex glass has become familiar to most of us as laboratory ware and domestic cooking utensils. The laboratory apparatus has given proof of its resistance to heat and chemical corrosion, and the baking ware has demonstrated ruggedness under constant handling. Sudden heat shock is also a feature of most of the domestic applications, the conditions frequently being more strenuous than in plant uses. A cold pie plate put into an oven heated to 400” F. has to meet a greater thermal shock than the large evaporating dish used on a steam bath in a chemical plant. 1
Consulting Engineer, Corning Glass Works.
The chemical properties which affect design are mainly corrosion resistances a t various temperatures. The mineral acids, with the exception of hydrofluoric and phosphoric, have no appreciable action on Pyrex up to their respective boiling points. Initially, there is a very slight surface attack, the figure for constant boiling hydrochloric acid being 0.000006 g., and for fuming sulfuric 0.000002 g. per sq. cm. per hr. This initial action is succeeded by a state of practical stability. I n the case of phosphoric acid, the attack produces crystallization at the glass surface and makes accurate determinations of solubility rather difficult. An average figure arrived a t by the Corning laboratories is 0.0027 g. per sq. cm. per min. Hydrofluoric acid does not attack Pyrex as readily as other glasses, this being a matter of knowledge possessed by all laboratory workers who have tried to etch beakers or flasks. The action is, however, sufficient to prevent any serious consideration of the use of Pyrex plant for hydrofluoric acid or fluoride production. Quite recently a question was raised as to the use of Pyrex in acetic anhydride manufacture, and it was found that no measurable attack occurred in 5 hrs. a t the fuming temperature. PRESEXT LIMITATIONS OF SHAPEAND SIZE Previous mention has been made of limits imposed by present processes of manufacture. Such limits are of considerable importance to the engineer who is considering, as a preliminary stage, the use of a new material for construction work. Without this information changes in the final design may be found necessary in order to bring certain parts within the existing limits of manufacture. Industrial Pyrex is made by various methods, the most important being pressing and blowing. Accessories for plant use, such as tees, tubulated vessels, etc., are produced in very much the same way as the smaller ordinary glass articles made by the laboratory glass blower, except that much higher temperatures are involved. Hemispherical evaporating dishes are examples of pressed ware, the largest available size being 24 in. in diameter.
