JULY 15, 1939
ANALYTICAL EDITION
405
Sealing wax (Dennison’s No. 391) is used to cement bushing C into the glass body, A . Mercury is placed in the portion marked Hg to act as a positive liquid seal, and to eliminate dead space.
hole. Rubber tubing 0.0625 inch (1.6 mm.) in diameter (spectacle tubing) is used for packing D,and is pretreated by immersing it in hot paraffin for 10 to 15 minutes and allowing it to swell to fit the hole counterbored in C. Because of variations in size of this type of tubing, the diameter of the hole in the bushing and the degree of swelling cannot be,stated very exactly, and some experimentation is necessary with each piece of tubing. No adhesive is necessary to hold the rubber in place, since the comparatively rough inner surface of the hole offers considerably more resistance to rotation than does the polished valve stem.
Literature Cited (1) Rangaswami, S., Proc. I n d i a n Acad. Sci., 8A,220-2 (1938). (2) Roth, H., and Daw, E. B., “Quantitative Organic Microanalysis of Pregl”, p. 83, Philadelphia, P. Blakiston’s Son & Co.,1927.
Handling of Hygroscopic Substances In the Microchemical Determination of Carbon and Hydrogen CLEMENT J. RODDEN, National Bureau of Standards, Washington, D. C.
T
HE various drying devices which have been described in
the literature for use in determining the amount of water in the microchemical analysis of a substance of type C (1) are oftentimes unsatisfactory when the anhydrous material is to be analyzed. The apparatus described below consists of a jacketed drying tube, so arranged t h a t i t may be kept at constant temperature, and a weighing bottle of special design. T h e sampie is dried, weighed, and htroduced into the carbon and hydrogen combustion tube without coming in contact with moisture at any stage of the operation. Figure 1 shows the apparatus.
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each weighing. The results have been corrected for zero variations and are the weights in milligrams in excess of the tare: 9.958, 9.980, 9.966, 9.964, and 9.965. The maximum variation from the mean is 5 micrograms. I n routine analysis of hygroscopic substances the variation in weight of the weighing bottle plus boat plus dry sample was seldom over 5 micrograms.
I n the course of an analysis, the weighing bottle with the empty boat is connected to F by means of a short length of rubber tubing which has been wiped out with glycerol and then with cotton. Air is passed through C, with D open, for a few seconds. The core, K , is turned by means of the handle, J , until closed and, after disconnecting, the bottle is wiped and weighed in the usual manner. n The sample is placed in the boat and an a p proximate weight determined. The boat is now transferred to the dryer and placed midway in chamber G . The liquid in the flask, I, is boiled and refluxed in B. The tube, E, containing the same desiccating agent as in C , is connected , ........I ......... to F, and a slow stream of dry air is sucked tL.........; ......... ........, through the apparatus by connecting H , which J also contains the same desiccating agent, to the K L M u vacuum line. D is closed during this operation. A “bleeder” may be used to obtain the desired vacuum. After the sample is dried, air is applied to C, stopcock D is opened, and air is allowed to escape through E. E is now disconnected and, while air is flowing, weighing bottle M is connected to F by means of the rubber tubing used before. The boat is removed to the N center portion of the weighing bottle by means FIGURE 1. DIAGRAM OF APPARA TU8 of a glass rod having a platinum hook fused into the end. Core K is now turned until closed off and the weight obtained as before. After the weight of the dry sample is obtained, A is essentially a Pregl microdesiccator, modified b y the addiit is transferred to the carbon and hydrogen apparatus as follows: tion of the jacket, G, and the side-arm drying tube, C, which is The stopper a t N is removed and with dry oxy en streaming from N the weighing bottle is attached by means ofthe rubber tubing filled with anhydrous calcium sulfate (indicating Drierite). By using an appropriate liquid, it is possible to keep the temperature previously used. Core K is turned until open and the boat is of the drying chamber constant over long periods of time without pushed into the combustion tube by means of a glass rod. The supervision. The adjustment of the flame is a source of trouble weighing bottle is removed and the stopper replaced a t N . in the original Pregl design in which a copper block is used to B y this method i t is possible to dry and analyze a substance, maintain a constant temperature around the tube. M is a weighing bottle of new design consisting of the shell, L, such as chrysanthemin chloride, which takes u p its water of the core, R,and the wooden detachable handle, J . L has two hydration almost instantaneously. short side arms of glass tubing, the same diameter as the dryer The apparatus may also be used for other purposes in and the combustion tube, N . The weighing bottle is constructed microchemical analysis, when i t is desired to isolate the subof soft glass. The core is greased with a light high-vacuum stopcock grease and the excess removed by wiping. Before use, the stance from moisture and carbon dioxide of the atmospherecore is rotated several times and the inner portion of the weighing for example, the determination of loss on ignition of limestone bottle wiped out with cotton. This is repeated several times to where the substance is weighed in the weighing bottle after ensure a clean inner surface. ignition in a quartz tube. The weighing bottle was tared with glass and constant Literature Cited weight was usually reached in 15 minutes. The weight could be decreased considerably by using a thinner rim. The (1) Alber, H.K.,Mikrochemie, 25,47 (1938). following values were obtained on the empty weighing bottle, PR~S~NT before E D the Division of Microchemistry at the 97th Meeting of the when the stopper was rotated and the bottle wiped between American Chemical Society, Baltimore, Md.
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