May, 1916
T H E J 0 L : R N A L O F I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R E’
a t high temperatures. This is easily shown in t h e pull-test, which is a simple method used by t h e glassworker for comparing the working qualities of glasses. The two glasses in cane or t u b e of t h e same diameter are sealed together and heated as nearly alike as possible a n d are then removed from t h e fiame a n d slowly pulled out a few inches, t h e joint being first slightly blown up in t h e case of tube. The harder glass will h’ave greater diameter a t t h e joint t h a n t h e softer after pulling out. This is a sensitive and very useful method for checking up t h e uniformity of different lots of glass. I n this test as already indicated t h e result in t h e case of glasses which differ widely in composition may depend on t h e temperature of pulling. A lead glass which appears softer t h a n a lime glass a t low temperatures may t u r n out t o be harder t h a n t h e same lime glass if t h e test is made quickly w h e n , t h e glasses are very hot. T H E T E N D E N C Y T O C R Y S T A L L I Z E is determined b y a method described b y Scha1ler.l X number of small crucibles containing t h e glass under investigation are maintained a t a low temperature favorable t o crystallization for a definite time, and t h e proportion of cases in which crystallization begins is taken as a measure of t h e tendency of t h e glass t o devitrify. R E S I S T A N C E T O A T T A C K B Y R E A G E N T S is most accurately measured by forming beakers of the glass and subjecting them t o t h e solvent action of redistilled water on t h e steam b a t h . The temperature thus attained is about 80’ a n d t h e usual time is 48 hours. The solution is evaporated in a small platinum dish a n d t h e residue weighed. Nonvolatile matter in t h e water used is determined a n d allowed for. Titration of t h e alkali dissolved instead of weighing is sometimes permissible b u t should be employed only for t h e comparison of similar glasses as t h e assumption is not always warranted t h a t t h e alkali found is proportional to t h e total amount dissolved. On t h e other hand, neither t h e alkali nor t h e total solids dissolved from t h e glass will in all cases answer as index t o t h e serviceability for t h e reason t h a t some glasses leave more opaque residue on dissolving than others do. The glass which is less soluble may become more cloudy when attacked by reagents t h a n t h a t which is’more soluble. For comparison in this respect we find a steam digester useful with pressure at about I O O lbs. A rapid method which has been very satisfactory consists in enclosing a short length of glass rod with I O cc. distilled water in a steel tube provided with screw cap and maintaining a t a temperature of 180’ C. for 2 hrs. The alkali in t h e water is then titrated. Eight or ten of these tubes are run a t one time. An unexpected result when, t h e glass baking dishes were p u t into service was t h e fact t h a t baking took place more rapidly in t h e m t h a n in dishes of t h e ordinary materials.2 Investigation developed a sufficient reason for t h e phenomenon but t h e fact was nevertheless very surprising. Metal reflects according t o various authorities from 83 t o 99 per cent of t h e radiant
’
L O C . Lit.
2
Sullivan and Taylor, LOC.c i l .
401
heat which strikes it while glass reflects only 3 to 14 per cent. T h a t radiation a n d not convection or conduction is t h e preponderant factor in baking was established by t h e following experiment: The reflectivity of a glass baking dish was changed in part from t h a t of glass t o t h a t of metal by silvering in a thin film on t h e outer surface in alternate quarters. A cake was baked in it in a n ordinary kitchen oven heated by a gas fiame. Where t h e cake had been protected by t h e metal coating, t h e bottom after baking was light-colored, sticky, and imperfectly ,baked, while in t h e other quarters it was brown and well done. As t h e cake was turned out bottom up the quartering was plainly visible on it. CORNIXG GLASS WORKS CORNING, N Y
A RAPID METHOD FOR THE DETERMINATION OF SOLUBLE NITROCELLULOSE IN GUNCOTTON By H. C. MALLINSON Received December 21, 1915
According t o t h e British Government specifications t h e determination of soluble nitrocellulose in guncotton is conducted as follows: “Four grams of dry guncotton are shaken up with 2 0 0 cc. of ether alcohol every 15 minutes for about 6 hours and then allowed to settle. When the solution above the guncotton is clear, 75 cc. are transferred t o a small weighed flask, the solvent evaporated, and the residue dried until constant in weight, at a temperature not exceeding 65’ C.” This method, which may be styled t h e evaporation method, is, to say t h e least, extremely tedious; a n d what is of more importance, it is not at all accurate owing t o t h e occlusion of solvent which cannot be driven off. A step in t h e right direction is t h e method used by some analysts in which water is added t o t h e solution before evaporating. This “indirect precipitation” method is as tedious a n d takes a little longer time t h a n t h e regular evaporation method, although t h e results are lower, denoting greater accuracy, for it is obvious t h a t if none of t h e ether alcohol-soluble matter is lost, t h e lower t h e results t h e greater t h e accuracy. It is our practice a t the laboratory of t h e smokeless plant of t h e American Powder Mills, t o determine solubilities by what may be called t h e “direct precipitation” method, which is not only much quicker but gives more accurate results. Some comparative d a t a (percentages) on different samples show interesting results: British Specification “Indirect “Direct Sample Evaporation PrecipPrecip;, Method itation” itation No. I . . ..................... 7.30 7.20 7.00 2.. ..................... 9.30 8.56 8.40 3 ....................... 20.00 19.22 18.82 4....................... 25.05(a) 24.26 23.82 (a)Obviously the error in the evaporation method increases as the solubility rises. By applying a correction, solubilities may be found by precipitation and made to agree closely with results obtained by evaporation.
The following results show t h a t repeated determinations are fully as satisfactory by t h e direct precipitation method as b y t h e other methods, t h e same sample of cotton giving: Direct Precipitation Method 26 16.84 16.84 16.88
“Indirect Precipitation” 17.20 17.66 17.36
Evaporation Method 18.08 18.16 18.10
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The evaporations were all conducted a t t h e same time and under identical conditions. I a m of t h e opinion t h a t if they were evaporated under different conditions of heat and humidity, these results would not check quite so well, while with our method there is no chance for conditions t o play a part. Another sample, treated according t o each of t h e three methods quoted below, gave these results: Percentages..
. . .. .. , . . . . . , ,
11 , 36
2a
2b
11.28
11.34
We carry out t h e direct precipitation method as follows : A j-gram sample (or if t h e solubility is known t o be z j per cent or higher, a 2-gram sample) is treated with 2 0 0 cc. of ether alcohol in a 2 0 0 cc. graduated cylinder. After settling, jo cc. of t h e supernatant liquid are transferred to a porcelain dish of 650 or 7 0 0 cc. capacity. About joo cc. of water a t a temperature of 7 j or 80' C. are slowly poured down the inside of t h e dish. This completely precipitates t h e dissolved cotton a n d t h e last traces of solvent are driven off by submerging with a glass rod t h e floating disk of cotton. The appearance of t h e precipitated mass determines t h e next step. I---Precipitate consists of one m a s s or d i s k ( o r o n e d i s k a n d a f e w s m a l l particles of cottoiz w h i c h m a y be added c o n v e r t i e d y l o the d i s k with f o r c e p s ) . The disk is removed and laid as flat as possible on a piece of filter paper which has been marked with t h e sample number, and rests on a folded towel or some other absorbent material. The sample is now moistened with alcohol t o shorten t h e time necessary for drying, covered with another filter paper, and t h e towel folded over all. By pressing with t h e hand t h e disk is dried t o such a n extent t h a t drying in t h e oven occupies b u t a very short time, about 2 0 minutes at 160' F. if t h e sample is not large. The t o p filter paper is removed before drying. t h e lower one with t h e sample being placed in t h e oven until curling a n d crispness indicate dryness. The sample is then transferred t o the balance and weighed directly. ( W t . i n g r a m s X 80 = Per cent soZutio?z.) z-Precipitate does not hold together a n d ( I ) i s i m p r a c tical. ( a ) Counterpoise two filter papers of conrenient size, fold, a n d place one within the other, putting both in a funnel. The mixture of water and precipitate is poured onto t h e filter, any traces adhering t o t h e sides of the dish being freed by a policeman. The dish is then rinsed with alcohol, and t h e alcohol poured onto t h e filter so t h a t it washes t h e cotton down into the apex of t h e cone. The filters are removed from t h e funnel, flattened out by pressing between t h e folds of a clean towel, then removed t o t h e oven. When dry, the sample is weighed by placing t h e outer filter paper on t h e weight side of t h e balance. Thus t h e weight is found directly. ( b ) A quicker and very exact method is to use a tared metal or porcelain Gooch crucible. Ordinarily this will suffice to hold the precipitate without a n y trouble whatever, and t h e bulk of the water may be poured through first. But if this seems inadvisable in certain cases, t h e largest mass may be transferred
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to the crucible, carefully covering t h e perforations; i t then acts as an excellent filtering medium, retaining t h e smaller particles when t h e remainder is poured through. The filtrate should be caught in a clean beaker and examined t o make sure t h a t it is free from precipitate. The mass is moistened with alcohol, t h e crucible placed on a clean folded towel, and the cotton is pressed first against t h e side of t h e crucible with a glass rod, then down on t h e bottom, somewhat after t h e manner of making a hfunroe crucible. 111 the case of an isolated sample, or when t h e cotton has been badly separated, a Munroe crucible may be used t o good advantage. Cotton treated by the direct precipitation method has much greater stability t h a n when evaporated from a n ether alcohol solution, and will stand a temperature oE 170' F. without loss of weight long after it is drv. E
X
Fig. 11: X,X'-Cross-section
of bar .4-Cylinder-section in place B-Hole in the bar through which the cylinder is inserted. C-A l/e in. hole at a right angle t o B. D-A loose-fitting rubber plunger. E-Screw for forcing plunger against A. F-Metal plate screwed to bar, threaded to fit screw E
Vre usually have results in half a n hour after drawing off t h e clear liquid, or in a n hour and a half after the dry cotton is p u t into t h e cylinder and t h e solvent added. Complete solution of the soluble matter is effected in less t h a n a n hour by placing t h e flasks in a revolving apparatus, instead of taking 6 hours when shaken 4 times per hour by hand. A revolving shaking apparatus may be obtained from any chemical apparatus dealer ( e . g., Eimer 8z Amend, N o . 6148). If the revolutions are 6 per minute, then the flask is inverted 3 6 0 times in a n hour. more agitation t h a n it would get by hand-shaking in 6 hours. We obtain t h e same results by attaching two boslike container? to t h e shaft of a water-wheel as in Fig. I. The cylinders are held in place with straps, and the wheel revolves five or six times per minute. An excellent apparatus for the purpose may be made from a 3-in. diameter wooden bar. Holes slightly larger t h a n t h e diameter of t h e cylinders are bored along t h e length of the bar, alternating a t right angles t o each other; if bearings are provided a t the ends one may be furnished with a handle for hand turning, a n d t h e other with means for attaching to or connecting with a motor (small electric or water) arranged to give from five t o ten revolutions per minute. Fig. 11 shows a way by Tyhich cylinders may be quickly inserted and held firmly in place. This can be easily made by any mechanic, and is quite as convenient and easy of operation as one obtained a t greater expense. MAYSARD, XASSACHCSETTS
