T H E JOVR,VAL OF I N D U S T R I A L A I Y D E-\''GISEERIn'G
150
creases to 0.3 ohm a t the maximum temperature. The furnace is operated a t 1300' C. (2372' F.), and since this is too high for the nichrome to withstand permanently, the latter is placed in the base of the furnace, where the temperature does not exceed I I O O O C. (2012' F.). The increase of resistance of the nichrome with the rise of temperature tends to offset, in some measure, the diminishing resistance of the carbons, and so to prevent any accidental overheating of the furnace in case of failure of the operator to look after the adjustment of the controlling device. The chief advantage of this plan over the rheostat is in the saving of energy. All the energy consumed is delivered t o the furnace, except the small amount (about 50 watts) required to run the motor, and the much smaller quantity required to actuate the switch. PHILADELPHIA, PA.
GAS BUBBLE AND WASHING TUBE FOR COMBUSTION APPARATUS By H. E. SMITH Received October 21, 1912
For several years I have used in combustion apparatus and for similar purposes a certain form of gas bubble and washing tube which has proved so very efficient and convenient that it may be of interest to other chemists. The tube is shown in the accompanying sketch. It will be seen that the entering gas bubbles through the liquid in one compartment, then is exposed to a large surface of glass pearls in another compartment. JULIO EUA5Cf
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The especial feature of the tube is that the spent liquid may be drawn out and the tube refilled without breaking the connections with adjoining apparatus
CHE;1lISTRY
Feb., 1913
or removing the tube from the train of apparatus. The spent liquid is drawn off by means of the stopcock after which the tube is recharged by removing the rubber stopper a t the top and running in the proper quantity of fresh liquid from a pipette. I t first moistens the pearls, then accumulates in the lower compartment. LAKESHORE & MICH. SOUTHERN RY. Co. COLLINWOOD,0.
A MODIFIED EXTRACTION APPARATUS By G . M. MACNIDER Received October 18, 1912
While there are quite a number of extractors now on the market for determining fat in solid substances, with each form there is some feature which is not entirely satisfactory when a large amount of routine work is t o be done. The Soxhlet and Knorr forms are probably most generally used. The siphon principle of the Soxhlet apparatus has been found to be most satisfactory for general work, but the cork or ground glass joints of this apparatus cause considerable trouble in setting up the apparatus and are frequently the cause of the loss of large amounts of ether. The Knorr form is superior t o the Soxhlet in that it requires about onethird the amount of ether for a n extraction and has only one joint, which is a mercury seal, thereby preventing the loss of ether. But the percolation principle of the Knorr is unsatisfactory on account of the difficulty in preparing satisfactory asbestos filters. The modified form described below was designed to combine the desirable features of the Soxhlet and Knorr forms. The apparatus consists of a small siphon extraction tube (Fig. I) which fits into the Knorr adapter in place of the I percolation tube used in the regular Knorr apparatus. The extraction tube is 8 cm. long and 2 cm. in diameter. The siphon is sealed into the bottom and rises to within I cm. of the top of the extraction tube. The details will be apparent from the cut. The sample to be extracted is contained in a S. & S. extraction thimble which fits closely into the extraction tube. I n this laboratory, extraction t h i m b 1 e s 19 X 90 mm. are used and the thimbles trimmed down t o a height of 80 mm. to make them flush with the top of 'the extractor. The extraction tube FIG.I1 'Ic I is shown in place in Fig. 11. As will be seen from the above, the siphon principle of the Soxhlet apparatus has been combined with the desirable features of the Knorr apparatus. As the extraction tube is small the extraction is done very rapidly so that the apparatus is well adapted to both
