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pipe bent t o give a horizontal tangential discharge against the wall of the tube. This tube was a 3-in. iron pipe, g1/2 f t . long, surrounded by a jacket through which hot oil was circulated. The liquid flowed as a thin film down the walls of this tube, and the vapors formed, together with the unevaporated residue, entered the large separating chamber below. This residue was continuously drawn off into the residue receiver while the vapor passed on t o the condenser and was collected as a liquid in the distillate receiver. Both receivers were provided with 'sight glasses t o observe t h e flow and gauge glasses t o show the volume. The' operation of this apparatus proceeded very satisfactorily and though all runs were short, it could easily be made continuous by installing duplicate receivers and reservoirs for stock. Several runs were made t o determine the most satisfactory conditions of temperature and rate of feed. The best run gave results as follows: Average temperatures: Bath of pre-heater and gas separator.. Bath around vaporizing tube. . . . . . . . . . . . . . . . . . . . Bath around residue separator. . . . . . . . . . . . . . . . . . . Mustard gas entering vaporizing tube. ............ Mustard gas vapor entering condenser. Average vacuum (absolute pressure), mm. mercury.. ... Average rate of feed, Jbs. per m i n . . . . . . . . . . . . . . . . . . . . Average rate of condensation, Ibs. per min.. Per cent of charge as distillate.. ..................... Purity of distillate (per cent mustard gas). Per cent of charge as residue.. ....................... Purity of charne (per cent mustard gas). Per cent of original mustard gas remaining in residue (by difference). ..................................
............
........... ...........
............ ..............
150" C. 183' C. 150' C. 147O C. 136' C. 60 0.95 0.51 53.5 92.5 40.6 81.5
32.0
Other runs were made under different conditions, with the following conclusions: ' I-Increasing the temperature at any point increased the decomposition, lowering the vacuum and lowering the yield. 2-Lowering the temperature a t any point reduced the yield. 3-Increasing the rate of feed did not increase the rate of distillation, and reduced the per cent yield. 4-Reducing the rate of feed increased the per cent yield, but not proportionately, and reduced the rate of distillation. I t was attempted t o reduce the rate of feed sufficiently t o .obtain a quantitative yield, but this failed; though the residue could be further concentrated by a second passage through the apparatus. It seems, therefore, t h a t the time required for complete evaporation of the mustard gas from the film of liquid is longer t h a n the time required for the t a r t o flow down the tube of given length. Accordingly, if the work had been continued on these lines, a tube of twice the length would have been built. As stated above, there was found t o be a considerable amount of material vaporized in the pre-heater and separated in the gas separator. This passed through a n air condenser, the condensate being collected in a receiver and the gas continuing through two wash bottles containing 1 2 per cent sodium hydroxide solution, which absorbed the hydrochloric acid. The gas then entered a condenser packed with crushed ice, and the condensate was collected in a receiver surrounded with ice. The residual gas, which was insignificant after the system was cleared of air, was bubbled through water t o indicate the amount. A
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typical run gave results, expressed in per cent of original crude mustard gas, as follows: Condensate, air condenser., , , , 1 . 8 Absorbed in alkali., . . . . . . . . . . 2 . 3 Light condensate.. , , , , , , , , , 1.4
.
.
Mostly HCI Smelled strongly of ether, b u t was decidedly heavier (0.81 sp. gr.)
If the temperature of the pre-heater was raised appreciably above 150' C., there was much more light material given off, and the liquid delivered t o t h e still was lower in temperature, due t o decomposition with absorption of heat. At lower temperatures nearly as much was given off. When material t h a t had once passed through the pre-heater a t I j o o was again put through a t t h a t temperature, there was practically no further evolution of gas. This indicates t h a t t h e amount first obtained originally existed in the crude material. It was desired t o make a further examination of these impurities and of the decomposition products, but very little of this was done, on account of lack of time. SMALL SCALE MANUFACTURING SECTION RESEARCH DIVISION, C.W. S., U. S. A. AMERICANUNIVERSITY EXPERIMENT STATION WASHINGTON, D. c.
AN AUTOMATIC COMPENSATING FLOW METER1 By 0.G. OBERFELLAND R. P. MASE Received January 4, 1919
The flow meter described in this article was intended primarily for accurately controlling the gas concentration of gas-air mixtures. By gas concentration is meant the amount of gas (either by weight or volume) per unit volume of gas-air mixture. The flow of t h e gas-air mixture is measured and kept constant a t all times. Hence the matter of gas concentration resolves into t h e problem of maintaining a slow and very cons t a n t flow of the gas. The principle of gas feed control, which is used in most laboratories, depends upon maintaining a constant gas pressure against a small capillary opening. The matter of maintaining a constant pressure in relation t o atmospheqic pressure is a comparatively simple one, since the use of a definite head of liquid through which a small amount of gas is permitted t o waste, suffices t o keep the gas pressure constant. However, i t frequently happens t h a t experiments require a n arrangement of apparatus in which the outlet end of t h e capillary is not against atmospheric pressure b u t against a pressure somewhat higher. I n such cases the pressure against the outlet of the capillary invariably fluctuates more or less. Hence the problem becomes t h a t of maintaining a varying pressure on t h e inlet of the gas capillary such t h a t the pressure difference between t h e inlet and outlet is always constant. The apparatus evolved for this purpose is shown in t h e drawing. The apparatus as shown is in reality two such devices. The advantages t o be gained b y t h e double arrangement are: first, t h a t the concentration of the gas in the gas-air mixture can be changed from one concentration t o another almost instantly; 1 Published by permission of the Director of the Chemical Warfare Service.
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and second, t h a t the apparatus can be used in maintaining concentration of binary gas-air mixtures. Referring t o the accompanying drawing, C and D are leveling bottles of 3 qts. capacity. The height of liquid in these bottles determines the constant pressure difference on the inlet and outlet of the capillaries. B is a supply reservoir for C and D. F and J are glass tubes of about 5 / ~ in. diameter. G and H are small glass tubes through which the excess gas escapes. These tubes reach nearly t o the bottom of C and D. X and, Y are the capillaries which admit the gas into the gas-air mixture line, a t t h e mixing chamber M . K and L are three-way capillary stopcocks which direct the flow of gas through the capillaries X and Y and overflow tubes G and H . The line W is coqnected t o the gas-air mixture line just ahead of the gas inlet by a glass “T.” It passes through a bottle of charcoal, 0 and-thence into the leveling bottles C and D.
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in C and D affords a measure of the pressure against the outlets of the capillaries of X and Y . The gas is permitted t o flow slowly through the valve of cylinder A or other gas supply and is conducted by a glass line and “T” t o the lower connections of stopcocks K and L. One of these stopcocks is set a t a 4 5 O angle (the one belonging t o the capillary not in use) thereby shutting off the gas flow, and the other is so placed t h a t the gas flow divides, part of it passing through capillary X or Y and the remainder through the overflow line G or H . The overflow gas bubbles out against the height of liquid in F or J above the level in C and D plus the height of liquid in C and D. As stated previously, the height of liquid C or D always counterbalances the pressure against the outlet of capillary X or Y . Hence the pressure difference on the inlet and outlet of capillary X or Y is always constant for all practical purposes and equal t o the pressure afforded by the height of liquid in C or D. W U H The proper size for capillaries X and Y t o give the AIR Sa-AIR 41XTURL required concentration must be determined experiH mentally. When one is found which is near the proper size the final adjustment is made by raising or lowering the level of the liquid in C or D. This is done by TO HOOD applying pressure or suction t o reservoir B and turning the stopcock E so as t o permit the liquid t o flow in 1 the proper direction. The function of charcoal in the bottle 0 is t o absorb any gas which might escape from the liquid in C or D and diffuse back into the gas-air line which leads t o the board. It is obvious t h a t the pressure compensation afforded by this device is not absolute since a rise of level in tubes F and J is accompanied by a fall of level in F bottle’s C and D. This fall is in proportion t o the relative cross sections of the tubes F and J and bottles C and D . The cross section of the bottles should be a t DAL least 5 0 times and preferably I O O times the cross section of the tubes. The apparatus as described was used in maintaining a I per cent concentration by volume of chlorine in a n air mixture. Analysis was made by the iodine titration method. The device was found accurate over any one day within “ 0 . 5 per cent and required little adjustment J , from day t o day. This serves as a good basis for judgment since the method of analysis is accurate. The device was also used in maintaining 0.1 per cent concentration by volume of another gas and was found FIG.1-AN AUTOMATIC COMPENSATING FLOW METER t o be absolutely satisfactory. The gas concentration When the apparatus is in use, the pressure in the was constant within the limit of error of analysis. gas-air line is communicated t o bottles C and D. With k gas supply of constant purity, adjustment of This pressure forces the liquid in C and D up into the level of liquid in the leveling bottle was not made tubes F and J until the height of liquid above the oftener than once or twice a week. The limit of error liquid levels in C and D counterbalances the pressure of the method of analysis with this latter gas was about * 2.50 per cent. However, i t is the consensus of opinin the gas-air line. It is evident t h a t any fluctuations encountered in the gas-air line, due t o any apparatus ion t h a t the variation of the 0.1 per cent concentrawhich may be attached to it, are thus registered by tion was much under this figure. The apparatus described was developed for use in the height of liquid in F and J above the liquid levels in C and D. This line pressure is the pressure which is connection with gas mask absorbent testing boards. against the outlets X and Y a t all times. Consequently, However, it is applicable t o any work which requires the height of liquid in F and J above the levels of liquid a n accurate regulation of gas concentration in gas mix-
-
RT
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tures or for control of rate of gas flow, as, for example, chlorination of natural gas and the determination of the heating value of gases. Acknowiedgment ;s made to the Gas Laboratory of the Pittsburgh Experiment Station of the Bureau of Mines for the pioneer work in applying flow meters t o
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measuring the rate of gas flow and the application of this principle t o testing gas mask absorbents and gas masks.
*.
GAS MASK RESEARCH DIvrsroN, c. w. s,, u. s. AMERICAN UNIVERSITY EXPBRIMENT STATION WASHINGTON, D. C.
ORIGINAL PAPERS THE GRAVIMETRIC AND VOLUMETRIC DETERMINATION OF MERCURY PRECIPITATED AS MERCURY ZINC THIOCYANATE1 B y GEORGE S. JAMIESON Received July 22, 1918
*
The methods t o be described are based upon the precipitation of the .mercury from mercuric compounds in neutral or acid solutions with a reagent which contained 39 g. of ammonium thiocyanate and zg g. of zinc sulfate per liter. The precipitate of mercury zinc thiocyanate was either weighed or titrated with a standard solution of potassium iodate in the presence of strong hydrochloric acid and an immiscible solvent such as chloroform in the same manner as recently described for the determination of zinc.2 I n order to get a quantitative precipitation of the mercury zinc thiocyanate there should not be more than 5 per cent of acid present in the solution before the addition of the precipitating reagent. Also i t should be observed t h a t in cases where larger quantities of acid are required for the solution of a substance the excess of acid should be neutralized with sodium hydroxide instead of ammonia because an excessive amount of ammonium salts exerts a solvent action upon the precipitate of the double thiocyanate. It was found t h a t cobalt, copper, bismuth, and nickel were partially precipitated along with the mercury zinc thiocyanate, and consequently, if present, they would interfere with the determination of the mercury. The volumetric procedure has been applied t o the determination of mercury in various kinds of antiseptic tablets and several other mercuric preparations with satisfactory results which are given below. I n order t o test the gravimetric method several solutions of mercuric chloride were * prepared and standardized by the well-known sulfide method. Measured volumes of these solutions were taken in perfectly clean, small beakers. Each solution was treated with 2 5 cc. of the reagent and diluted so t h a t the final volume would be about 7 j cc. The solutions were vibrated by striking the sides of the beakers with a stirring rod t o facilitate the separation of the crystals. After the solutions had stood for about j min. they were briskly stirred with a glass rod, previously moistened with water, for about a minute. This treatment permitted the rod t o be easily rinsed free from the precipitate so t h a t it could be removed from the beaker. The solutions were allowed t o stand a n hour or longer before filtration. The precipitates were collected on Gooch crucibles and washed four or five times with a washing solution which contained 5 cc. 1
Published by permission of the Secretary of Agriculture.
2
J A m . Chem. Soc., 40 (1918), 1036.
of the thiocyanate reagent and 450 cc. of water, on account of the solubility of the mercury zinc thiocyanate in pure water. The crucibles containing the precipitate were dried for a n hour between 1 0 2 ' and 108' C. and weighed. The mercury was calculated by multiplying the weight of the precipitate by the factor 0.40258. The dried double thiocyanate has the composition HgZn(SCN)4. The following results were obtained: No.
........
H g Taken
Gram
HgZn(SCN)'a Gram
0.0402 0.1239 0.1328 0.1118 0.1451 0.1209 . O . 1360 0,0907
0.1006 0.3082 0.3305 0.2783 0.3605 0.3009 0.3385 0.2246
I.. 2. . . . . . . . . . 3.......... 4
.......... S...... . . . . 6 .......... 7 . . ......... 8 ..........
Hg Calculated Gram 0.0405 0.1240 0.1327 0.1120 0.1451 0.1211 0.1362 0.0904
Error
Gram -~ +0.0003 ~~
+O.OOOl -0.000 1 $0.0002 0.0000 +0.0002 +o .0002 -0,0003
I n Analysis 8, the precipitate was allowed t o s t a n d for only half an hour instead of a n hour or longer as recommended above. The test analyses show t h a t satisfactory results can be obtained by this method. I n order t o test the volumetric method for the determination of mercury when precipitated as t h e double thiocyanate, two solutions of potassium iodate were used. The first one which had been made for another purpose, contained 39.2882 g. of KIOa in 1000 cc., and the second one, specially prepared for this investigation, contained 19.2191 g. of KIOs in 1000 cc. According t o the equation
+ 6KI03 + IzHCl = HgS04 + ZnSOl + + 4HCN + 61C1 + 6KC1 + 2HzO
HgZn(ScN)e ~HzS04
the first solution will have I cc. equivalent t o 0.006133 g. of Hg and the second solution will have the value I cc. = 0.00300 g. of Hg. Measured volumes of the standard mercuric chloride solutions mentioned above were precipitated and allowed t o stand as previously described. The solutions were filtered on 7 cm. washed filters, using gentle suction. The precipitate adhering t o the beaker was transferred t o the filter by means of a small wash bottle containing I O cc. of the thiocyanate reagent and 4 j o cc. of water. Then the filters were washed around the upper edge four times with small quantities of the washing solution. When the filters had drained, the suction was stopped. The filters were carefully removed from the funnels and were folded so t h a t they could be placed in 8 oz. glass stoppered titration bottles. A thoroughly cooled mixture of 3 5 cc. of concentrated hydrochloric acid and I O cc. of water along with 7 cc. of chloroform was added t o one of the titration bottles containing mercury zinc thiocyanate, because it is best t o titrate immediately after adding the acid t o the precipitate. During the first part of the titration the potassium
