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mentioned anti-dimming compositions. The third material, RIo, was one of many commercial preparations which had been tested. TABLEIX-PERCENTAGE GAIN IN WEIGHT OF DR\ED COMPOSITION WHEN EXPOSED TO MOISTAIR AT 35 C. TIms MIN. NEWSTICK PASTE RIQ 15 18’ 4.3 9.9 6.6 13.2 30 42 60 .... 24.0 .. 14.9 56.5 120 210 24.5 1 Time was 10 min. This sample could run only 35 min. (gain 48 per cent) as the surface tension of the film was so low that the water ran off the eyepiece.
.. ..
....
The materials are arranged in the order of their efficiency in preventing dimming, the new stick being the best. These d a t a show t h a t the composition best for use in the gas mask absorbed moisture most rapidly and lowered surface tension most, but for the other two materials moisture absorption did not run paralld t o efficiency in preventing dimming. Another line of work in which some progress was made was t h e attempt by K. Flynn t o evolve a rapid method for control testing of the product for its inspection before acceptance. Air, a t measured velocities, was bubbled through hot water and then passed through a jet t o impinge on the eyepiece t o which the material t o be tested had been applied. The temperature oE the water was maintained a t the approximate temperature desired, by regulating the size of flame. Inside the boiler the air had t o pass through water a t a n approximately constant level and through screens above the water t o aid in saturation. The eyepiece was held in a frame soldered into the wall of a tin can having a glass window directly opposite. The can contained ice and water which were stirred. The temperature was measured by a thermometer directly in front of the eyepiece and in the path of the jet of warm, moist air. The following results were obtained using WI,, a laboratory preparation made with Turkey red oil. The time given was from the start until the soap film had broken on two-thirds of t h e lens, so t h a t the water conderised in drops. TABLEX-METHOD FOR CONTROL TESTING A-Effect of Rate of Flow of Moist Air RATEO F FLOW TIMEIN MINUTES L. per Min. 94’ F. lZOo F. 2 6 8 11 15 18
48 38
.. 30 .. 26
..
29 19 12 (12 1. per min.) 9 5
B-Effect of Temperature TEMPERATURE TIME IN MINUTES Deg. F. 1 1 I,. per Min. 18 I,. per Min. 90 .. 30 30 26 (95 94 28 16 (lO;°Fd.) 98 15 10 110 10 5 120
Rates of flow above 18 1. per min. or temperatures above 1 2 0 O F. gave variable data. The time became somewhat greater with either change, due t o the fact t h a t i n these cases a smaller fraction of the moisture carried by t h e air was being condensed by t h e lens because more escaped t o the sides. Using this method three compositions were tested with the following results:
TIMEIN MIN. S t i c k . , . . . . . . . . . . . . . . . . . . 34,35, 28 W,,...................... 6, 5, 8 Paste .................... 73, 77, . . T 5 120° F.; flow 18 1. per min.
-
The method in this form was, therefore, not suitable for testing, as the order of merit for these materials was: stick, WIG, paste, the last being the poorest one. A t least one trouble lay in the definition of the endpoint, but further work was interrupted by other problems. RESEARCH DIVISION CHEMICAL WARFARE SERVICE AMERICAN UNIVERSITY,WASHINGTON, D. C.
ANTI-DIMMING PREPARATIONS FOR GAS MASKS By HARRYN. HOLMES, F. F. JEWETT,GLADYS LEAVEL~, DORTHA BAILEY AND EDNASHAVER Received July 31, 1919
The National Research Council requested t h a t a study of anti-dimming preparations be taken up in order t o supplement the work of Captain Carleton, Private Woodside, and others ‘of the Research Division of the Chemical Warfare Service. I n particular i t was suggested t h a t the function of sulfonic acid groups be investigated, the effect of their number, position, etc., and also t h e effect of molecular weight. I n general i t was desired t h a t the theory of the action of anti-dimmers be worked out as far as possible, t o the end t h a t in the light of a clear understanding of their action better and cheaper products might possibly be devised. To this end a somewhat detailed study was planned as follows: I-Of the sulfonated glycerides of saturated and unsaturated fatty acids as well as sulfonated fatty acids. 2-Of the relative merits of potassium, sodium and lithium salts of sulfonated fats. 3-Of soaps of saturated and unsaturated fatty acids. 4-Of Twitchell’s sulfo derivatives. 5-Of the effect of excess base, glycerol, mineral oils, water glass and fillers in preparing anti-dimming sticks. 6-The relation of surface-tension lowering to the desired anti-dimming effect. 7-The influence of solubility on the lasting power of antidimming sticks. 8-The effect of varying thickness of the anti-dimming film. 9-More rapid and more accurate methods of testing. DROP-SPREAD TESTS O F SURFACE-TENSION LOWERING
As a method of rapid preliminary testing the “dropspread test” was designed. This was based on the theory t h a t anti-dimmers lowered the surface tension of the drops of moisture condensing on the eyepieces so t h a t these drops spread t o a smooth film permitting clear vision. Therefore, any method of measuring surface tension could indicate the possible value of a given substance as an anti-dimming material. The rise of solutions in capillary tubes was too tedious. The spread of a falling drop of water on a glass plate which had been rubbed with a n anti-dimming preparation served as a very rapid, though approximate method of selecting materials for the subsequent slower but more accurate tests. The drop was allowed t o fall a distance of 8 mm. from a burette t o a level plate. The filrr of material on the plate was rubbed by rotary
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motion until thin and nearly dry. A wet plate causes the falling drop to spread. We found t h a t drops spreading t o a diameter of about 2 0 mm. or more indicated a substance of such good surface-tension lowering power t h a t further testing was advisable. On clean, dry glass a drop spreads t o a diameter of 8 or g mm., slightly less on a celluloid or cellon surface. WINDOW PANE TESTS
I t is evident t h a t all methods of testing with gas masks are inconvenient because if a single observer d s e s the work the time involved in a large number of tests is excessive. Moreover, the physical discomfort is great. With a long series of comparative tests lasting days, weeks or even months, the observer’s own standards of visibility fluctuate. With one observer only very few tests in a day are possible. If, as was done by previous investigators, a number of men made the various observations, then the personal differences in eyesight, standards of visibility, etc., made any very accurate comparison impossible. The ideal method for the preliminary testing, then, demanded t h a t a single observer make a large number of readings within the space of an hour or less, and also t h a t the observer should not be severely taxed physically. It occurred t h a t the use of a small room with many small window panes, a pan of boiling water, films of anti-dimmers on the windows, an observer in the room and an assistant outdoors t o hold a printed chart and measure distances along a steel tape, met all these requirements. Preliminary trials showed that a large window pane was of no use as the moisture condensing above a treated spot ran down, spoiling the test. Hence the value of windows containing many small panes. Two or three different anti-dimmers could be rubbed on each pane just under the horizontal framing a t the top. As a result each spot held or ran on its own merits. It was a simple matter t o boil enough water into the air of the small room.to insure condensation on the windows in any desired amount. Cold weather favors such condensation, of course. The windows must be tightly packed around all cracks as a current of incoming air drives the moisture from the windows. I n this connection we found an excellent endorsement of the placing of the air intakes in the Tissot mask directly against the eyepieces. I n the room selected for our experiments the upper window contained small panes but the lower held only one large pane so we reversed the windows. To our surprise parts of the surfaces on the lowered window would not.condense a dew even where no anti-dimmer was applied. Investigation revealed a wide crack between the two windows. When this was stuffed with rags condensation became normal. The current of cold, dry air from outdoors falling down over the glass had effectually prevented condensation. Cracks a t the side of the window frame also needed stuffing. The assistant outdoors measured off distances along a tape and moved a chart as dgnaled from the observer in the room. When letters on the chart could be read with difficulty the distance was noted. A compari-
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son of these distances for any given set of readings furnished a measure of the relative film-forming efficiency of anti-dimming substances tested. By taking sets of readings a t intervals of 2 0 min. the lasting qualities of the films were plainly shown. Although moist, the room was comfortable, and, in fact, the observer could leave the room for rest intervals in a dry atmosphere. After some practice we learned t o make 56 readings in 15 min. Quick decision and effective signaling were necessary. The great advantage, in accuracy of comparison, of such a large number of observations made in 15 min. by a single observer is evident. I n t h a t short interval errors from changes in the light outdoors are small. Of course, the actual distances are not t o be compared in readings made on different days, due t o changes in the light, but the order of merit in successive series of readings may fairly be used for comparison. I n a word, the room serves as a giant mask with windows for eyepieces, b u t with 56 eyepieces instead of one pair. The observer is within the great mask, although not fitting i t very tightly, and is decidedly more comfortable t h a n t h e masked soldier. Instead of laboring to perspire, a steam pan saturates the atmosphere for him. The anti-dimming material should cover a spot about 4 in. wide, so t h a t both eyes can be used in reading. The material is applied with a glass rod, or cork, and rubbed with soft tennis flannel t o a layer almost invisible, aided by occasional blowings of moist breath on the glass. The official method of rubbing with the finger obviously leads to mixed results when several different substances are studied a t once. We found 2-in. squares of the flannel quite suitable. INFLUENCE OF THE SULFONIC ACID G R O U P
Using
the
“drop-spread”
device
we
discarded
Sodium ethyl sulfate Potassium ethyl sulfate Aniline sulfate Sodium and potassium sulfanilate Sodium @-naphthalenesulfonate Potassium isobutyl sulfate Light and heavy petroleum oils Fats Saccharine Many esters, alcohols, aldehydes, amides, sugars, hydrocarbons, and phen o1s Several naphthalene products containing the -“a, -OH and --SOxH groups.
Good drop-spreads induced us t o test further t h e following : Sodium benzene sulfonate, to which we added the di- and trisulfonic derivatives Sodium toluene sulfonate Glycerol Sodium products of egg albumen Saponin Sodium ethyl sulfonate Twitchell’s sulfo derivatives Soaps Alkali salts of sulfonated fats A naphthalene derivative containing the amino, hydroxyl, and sulfonic groups in 1,2,4-positions.
These were tested repeatedly on the windows of the steaming room. None of the true sulfonic acid
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compounds stood the window test, in some cases because of too great solubility. From the drop-spread and window tests i t is evident t h a t organic sulfates are not necessarily effective as a class; t h a t the mere presence of a sulfonic acid group, either in aliphatic or aromatic compounds, has but little t o do with film-forming capacity; t h a t the number and position of sulfonic acid groups are of small importance, in fact sodium benzene disulfonate and trisulfonate were worse t h a n sodium benzene monosulfonate; t h a t the naphthalene ring sulfonates are no better t h a n t h e benzene ring sulfonates; t h a t the presence of the amino and hydroxyl groups is of no material aid. It is admitted t h a t a few of these substances functioned moderately well as anti-dimmers for a few minutes, but they had no staying powers. I N F L U E N C E OF F A T S , OILS, ETC.
A number of mineral oils were tested, vaseline included. We were tempted t o t r y them because of the smooth transparent films formed. As film-formers they were all decided failures. Liquid fats seemed worth trying for the same reason, but they also were failures. The moderate film-forming efficiency of glycerol and the high efficiency of saponin solutions indicated t h a t the film-forming effect is not a function of a n y particular class of compounds except the group t h a t lower!; surf ace tension considerably. Saponin and glycerol have this effect, as is well shown by the rise of their solutions in capillary tubes. At this stage i t became clear t h a t all anti-dimmers must lower surface tension of water decidedly but t h a t those t h a t dissolve too rapidly fail because of their quick removal from the eyepiece. Also those t h a t dissolve too slowly may fail. Twitchell’s benzene-stearosulfonic acid and the similar compound made by treating oleic acid and naphthalene with concentrated sulfuric acid seemed very promising, but as film-formers they were only fair. Dropspreads were good, and their high molecular weight and sulfonic acid groups and f a t t y acid residue combined t o make a careful test interesting. I N F L U E N C E O F SOAPS
Since alkali soaps as a class lower surface tension decidedly they were tested carefully. As a class, soaps derived from glycerides of the saturated f a t t y acids gave poor results and soaps of unsaturated f a t t y acids were superior) some. of them showing up in the window tests even better t h a n the anti-dimmer officially adopted. But there were exceptions. Cod soap was not effective, yet t h e clupanodonic acid and therapic acid of cod oil are more unsaturated than any other fatty acids. Linseed soap and rape soap were excellent, making a better showing t h a n the official anti-dimmer. The acids of linseed oil are highly unsaturated, and the oil has a high iodine number, but rape oil has only about half the iodine value of linseed, and yet its soap was found t o be just as effective. Corn soap and castor soap were very good indeed, as might have been
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predicted) for their acids are unsaturated. Yet peanut oil has almost as high a n iodine number as rape oil and peanut soap was poor. Soy bean soap (the oil has a rather high iodine number) was moderately effective. Ivory soap was ineffective but a “super t a r ” transparent soap made by Armour and Company was fully as effective in our tests as was t h e official anti-dimmer. It had one serious fault, otherwise i t might be considered as a substitute for the anti-dimmer now used, since it makes a solid stick and the film lasts well. Unfortunately, however, a whitish deposit is left on the glass and with repeated applications this might accumulate t o a disturbing extent. A number of soaps were distinctly improved by the presence of a little glycerol, either left in by limited washing or some added t o a well-washed soap. Corn soap serves as a good illustration. One sample of corn soap was acidified to liberate the acids. These washed acids were then neutralized with sodium hydroxide, thus forming a soap free from glycerol. This soap had very poor film-forming power but if a few per cent of glycerol were added the results were greatly improved. Soaps in general were improved by the addition of from I O per cent t o 1 5 per cent of sodium hydroxide. A “marine oil” secured from the Standard Oil Company improved soaps, if present t o the extent of about 3 per cent. This oil, which emulsifies in water with wonderful ease, has itself very fair film-forming power, especially if a water emulsion of i t is applied in a very thin film. To make solid sticks of soap, about 3 per cent water glass syrup was helpful, acting as a binder as well as a solution restrainer. I n making these soap sticks we weighed t h e ingredients, dissolved the soap in a little hot water, stirred in the concentrated sodium hydroxide, water glass syrup, marine oil, and glycerol, and evaporated off water until the mixture became the right consistency t o press into molds. As a laboratory device we used a cork borer 8 mm. wide for the mold. Filling this with the mixture we held i t firmly against a block of wood and hammered in a steel rod t h a t fitted the mold. Then it was a simple matter t o push out the stick of soap mixture on a glass plate t o dry. Wrapped in tin foil i t was ready for use. Some soaps are brittle when dried, so a stick 1 2 mm. in diameter is recommended, as i t is less likely t o break with rubbing. Rape soap makes a brittle stick but linseed soap and corn soap sticks are strong. The relative merits and composition of these soap sticks will be listed with the sulfonated products on a later page. SULFONATED PATS
Although Turkey red oil is termed a “sulfonated” f a t i t is really a primary ester of sulfuric acid mixed with some other products. On boiling with water, free sulfuric acid and a hydroxy acid are formed. Sulfonated castor oil, wholly or partly neutralized by sodium hydroxide or ammonia, is the product preferred in the dye industry but similar Turkey red oils have been and are made from olive oil, cotton oil, corn oil, etc. I n practice the concentrated sulfuric acid is allowed:
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t o run into the oil slowly, with constant stirring, taking care t h a t the temperature of 35’ C. is not exceeded. This temperature regulation is most important. The product is then rinsed with a small quantity of water and the dilute acid allowed t o settle out. The lower layer is drawn off and the oil washed with a solution of Glauber’s salt until the washings are only slightly acid. The commercial product is often only partly neutralized. We prepared our own sulfonated oils a n d neutralized completely with sodium hydroxide. Most of our products contained about 3 5 per cent water. Much of this was added in neutralization as i t is not difficult t o obtain an 8 5 per cent Turkey red oil (acid). The free fatty acids may also be sulfonated but not so easily as t h e glycerides. Glycerides of saturated f a t t y acids are not readily sulfonated. The attack is on the double bonds of unsaturated acids forming primary esters of sulfuric acid. Castor oil differs from other fats in t h a t its acids (chiefly ricinoleic) are not only unsaturated but hydroxy acids. If t h e excellent film-forming properties of salts of this Turkey red oil are due t o hydroxy unsaturated acids then no other sulfonated fat could compare with it. And if t h e effect is due merely t o the presence of unsaturated acids then almost any sulfonated unsaturated f a t should have value in this connection. This conclusion led us t o test Turkey red oil soaps made from Castor oil Cotton oil Rape oil Corn oil
Linseed oil Olive oil Cod oil Olein
All of these, except cod oil, yielded effective filmformers. We do not understand the failure of cod oil as it has a very high iodine number. Possibly further work might clear up this point. The free acids from cotton oil were sulfonated and the sodium salt proved effective as a film-former. Ricinoleic acid was isolated from castor oil and sulfonated. The sodium salt showed up well as a n antidimmer, but no better t h a n a number of other products. Previous workers had declared the effect of sulfonated castor oil was improved by adding 1 5 parts sodium hydroxide t o IOO parts of 85 per cent sulfonated oil. We varied the proportions and finally adopted I 5 parts sodium hydroxide t o I O O parts of 65 per cent sulfonated fats (alkali salt). I n the case of sulfonated rape oil we increased the proportion of base t o 2 0 parts. This makes our products more alkaline t h a n t h a t officially adopted. We found 3 parts of water glass syrup t o IOO parts sulfonated oil sufficient for binding purposes. Contrary t o the experience of the previous workers we found glycerol (about 3 parts t o 100) a distinct help. Also contrary t o the experience of previous workers we found paraffin oil (such as Nujol) of very little value. It has no film-forming properties of its own, in fact has no effect in lowering surface tension. We replaced i t by another oil with all the good properties of paraffin oil and none of its defects. This was I
