llian 2 per cent chromium; for snrnples of larger clironiium wntent a 1-gram sample is suitable. Place it in a BOO-cc. beaker, add 15 ce. of water, 15 ec. ortlviphosplioric acid, sp. gr. 1.37, and run in a measured volume of sulfuric acid, sp. gr. 1.83, from a buret. i\llow 1.5 cc. of acid for ea.ch gram of steel and 3 ec. excess. After the steel has been completely decomposed, boil until a considerable quantity US salt, separates out, in order to assist in decomposing carbides. Dilute with 20 cc. of water and heat until tlie salts !iai-e dissolved. Add nitria acid, sp. gr. 1.42, drop by drop, l o the hot liqnid until the viulcnt oxidation of ferrous sulfate is oyer ( 2 t,o 3 cc. of acid are sufiicient; aroid any appreciable excess). Roil the solution to destroy oxides of nitrogen, dilutc to 150 cc., heat tu boili~ig,add 10 ce. of silver nitrate containirig 2.5 grams AgXOa per liter, and 1.5 grmu OS amiiiuniurri persulfate. If no perrriangnnate tinge appears in tlic solution on boiling, add inure ammoninm persulfate. In no case will more then 2 to 2.5 grams be required if samples of tlie weights suggestcd above are used. Boil the solution for 10 minutes t o decompose the excess persull'ate, dilute to 200 cc., heat to boiling, add 5 ce. of 1:shydrocliloric acid to reduce permanganate, and boil vigorously for 10 minutes to r m o r e elili~ri~ie,Add to tlre solirtion at rooin temperature
that quantity of crystdized sodium acetate ~vhiehis required to react with the excess of sulfuric acid used in dissolving tho steel. (1 cc. of concent,rated sulfuric acid is equivalent t o 4.8 grams of sodium aceiate trihydrate.) As soon as this has dissolred, add 0.6 to 0.8 cc. of 0.1 per cent diphenylbenaidine solution (prepared by dissolving 0.1 gram of the reagent in 10 cc. of coneent.rated suliuric acid and diluting this with '30 cc. of glacial acetic acid), nlloiv 5 miniitcs for the color t o develop, and titrate with 0.05 .V ferruiis snllilte. The corraction to be applied for the im1ic:itor is added to tlie volume of ferrous sulfate and :mounts to 0.015 cc. of 0.05 .\ ferrous sulfate per 0.1 cc. of indicator. In Table 11, 1.5- to %gram sarnplcs were u w l .
li.
Of
s. so. a0
!,',(1.02,A
cri
Per ceni I . 03 l.OZ
1.04 1
II.
Of
s. s o . 72
2.31 3.34 L 34
(0.81% Cd
Prr Cent 1 02
I.U%
1.04 2.33
2.34 0.Sl 0.01
Carbon Resistor Furnaces for Laboratory Use' 1% C. Kremers and L. U N I V B K S L T I OP
F. Yntema
IiLreurs, IlarraNr,
T
HMZE is ol'ten need for il furnace t!iat will mainbin a higher temperature than can be attained with nickelchromium alloy resistance units. Tungsten or molyhdenum may be employed, but the obvious disadvantage is that the units must be kept in a hydrogen or inert atmosphere. A plat,inum-vound furnace is expensive. A granular carbon resist,ance furnace offers the advantages of low initial cost; high t e m p e r a t u r e s , limited only by the n a t u r e of the refract o r i e s employed; and ease of operation and r e p l a c e m e n t of the h e a t i n g u n i t . Thc principle may be applied to tlie construction of either a pot or a tube furnace. For a pot furnace two c o 11 ccn i r i c alunduni tubes 12 incheslong (1) lire mounted vertically on a graphite bar ( 2 ) and the space between Figure I--Diagram of Furnace the tubes is filled to within 4 inches of t.he top, with a '/a- t o '/&inch granular carbon (3). . A grapiiite collar (4), to which one of t.he power leads @),isattached, makes contact with the granular graphite. The other lead (5) is attached to the lower end of the graphite bar. The graphite bar rests on an iron plate suspended from the *Received March 20, 1928. Presented before the Division of Iildustrial and Engineering Chemistry at the 75th Meeting of the Amrticim Chemical Society, Sf. Louis, Mo., Apr3 10 t o 18,1928.
ILL
b m holding t,hc insulation, ami an iron c d I u with wings (ti) rests on the graphite collar making contact vith the granulnr carbon. By changing the pressure on the collar the coliductivity of the furnace may be varied. In order to reenforce the outer of the two alundum tulles, an iron pipe ( i ) 2 inches greater in diameter is supported externally around the tube and the soace filled with alundum cement. The upper and lower enis of the box may conv e n i e n t l y be made of c i r c u l a r disks of transite and the side wall of heavy galvanized sheet iron. The insulation is an asbestos-Sil-o-Cel inixture. The furnace is best ruii with a step-doan transformer, with a variable s e c o n d a rg winding. A furnace m a d e of a l u n d u n i tubes of 3 and 5 inches i n s i d e diameter, respectively, r e q u i r e d 50 volts on the secondary t' give an inFigure >Furnace and Step-Down put of 3 kilowatts, by 'rransformer. ~ u r n a c c Censtrurfed of 3and 5-Inch Tubes a hmperature of 1000" C . may be reached in less than 1hour. Wlien that temperature is reached 30 or 40 volts on the secondary will hold it constant. A furnace constructed of 1.5- and &inch tubes requires proportionally less power to operate. A tube furnace vas made with a 2-inch outer tube 12
INDUSTRIAL AND ENGINEERING CHEMISTRY
July, 1928
inches long and a 1-inch inner tube. Contact is made with the granular carbon packing on each end by graphite collars that may be tightened by thumb screws. Otherwise the construction is very similar to that of the pot furnaces. Sei-era1of these furnaces have been constructed in this laboratory and have given satisfactory service under widely
771
varying uses. Temperatures of 1200" C. have been maintained for hours. The granular carbon must be replaced occasionally, but that is very easily done by pulling out the inner tube, taking out the old carbon, screening out the fines and repacking. These furnaces are splendidly adapted for alloy research.
An Improved Gas Generator' V. T. Jackson UKIVEKSITY O F FLORIDA, GAIKESVILLE, FLA.
H E gas generator for hydrogen sulfide, described herein, has been used in the qualitative analysis laboratory of the University of Florida for several months. It has required a minimum of care and proved very satisfactory. The stand for the generator is shown in Sketch I. The bottom, shelf, and sides are made of 10-inch (25.4-cm.) boards. The bottom is 24 inches (61 cm.) long. The sides are 31 inches (78.7 cm.) high. The s i d e s a r e f a s t e n e d 2 inches ( 5 cm.) from the ends of the bottom. Holes are bored through the ends of the bottom for screws to fasten the stand to t h e t a b l e t o p . The s h e l f , A , is p l a c e d 7 inches (18 cm.) from the tops of the sides. A 3-inch (7.6-cm.) hole, with beveled edge, is bored 4.5 inches (11.4 cm.) from the r i g h t hand end of the shelf. -4 1-inch (2.5-cm.) hole is bored to the left and in front of this hole. The Sketch I strips B and C and the cross strip BC are made of 1-inch (2.5-cm.) square lumber. The complete generator is shown in Sketch 11. D and E are 8-liter aspirator bottles, with an opening near the bottom of each. F is a 2-liter acid bottle. L is a \Tide-mouth bottle; it should have a capacity of at least a liter, preferably larger. The bottle F is fitted with a 2-hole rubber stopper. A length of 3 mm., inside diameter, glass tubing, G, is passed through one of these holes so that its outer end extends just beyond the stopper; the other end should reach nearly to the bottom of the inverted bottle. The glass tube J , 8 to 10 mm. inside diameter, should juqt pass through the other hole in the stopper in F , and should reach to the T-tube I , to which it is joined by a rubber connection. The tube N is joined to the other end of the T-tube by a rubber connection and is extended to the bottom of E. The glass tube K , inside of the bottle E, of 20 mm. inside diameter, should extend from the bottom of the bottle to within 10 to 15 em. of the neck of the bottle. Glass and rubber tubing of the same size as the tube J should connect the lower opening of the bottle D with the free arm of I . A Hoffman screw clamp is placed over the rubber tubing at H . The glass tube M should be of the same size as J . It should barely pass through the rubber stopper in the mouth of E , and should go to the bottom of L. Four holes should be bored in the rubber stopper for the
T
1
Received February 13, 1928.
bottle L, for stopcocks, which are bent and inserted as indicated. Pieces of rubber tubing, of such length that they will not quite touch the bottom of the stand, are fastened to the free ends of the stopcocks. A glass tube is attached to one of these when one wishes to use the gas. A 1-hole rubber stopper, through which is passed a 6-em. length of glass tubing of the same size as J , is inserted in the hole (not shown in sketch) near the bottom of E. A 60-cm. length of rubber tubing is attached to the free end of the glass tube, which is closed with a Hoffman screw clamp. The bottle E is filled to a depth of about 8 cm. with broken glass. The tube K is then placed in position as indicated. The bottle is then filled to the height of K with ferrous sulfide, and over the top of this is placed a layer of glass wool. The bottle is then closed with the rubber stomer, - _ bearing- the two indicated t u b e s . The bottle L is filled two-thirds with g l a s s wool, r a t h e r t i g h t 1y p a c k e d , and the remaining space with cotton, loosely p a c k e d . This prevents s p r a y from being carried over into the precipitating vessel. The bottle D is filled with dilute hydrochloric a c i d . T h e screw clamp a t H is t h e n o p e n e d and the bottle F is filled about one-third with the acid. One of the stopcocks is then opened a n d t h e acid is allowed t o flow into E . When the Sketch I1 stopcock is closed, the acid FTill generate enough gas, by its action on the ferrous sulfide, to push the acid into F . lT7henthe acid is spent, it may be readily drawn off through the rubber tubing attached to the bottom of E. One filling with ferrous sulfide will last for a t least a year. There is no waste in drawing off the spent acid. It is desirable to precipitate with hydrogen sulfide under pressure. This is done by fitting a conical flask with a 1-hole rubber stopper and passing a 5-cm. length of glass tubing barely through the stopper. The free end of the glass tube is attached to the rubber tubing, fastened to one of the stopcocks. The flask should be opened for a few seconds, to allow the escape of air, after the gas has been turned on. By substituting marble chips or zinc for the ferrous sulfide, a very satisfactory generator for carbon dioxide or hydrogen is made. I
