1090
INDUSTRIAL A-VD ENGINEERI-VG CHEMISTRY
the inlet of the gas meter Till change the volume of gas delivered to the burner unit owing to change of water level within the meter, and will therefore affect the heating values recorded. It was considered desirable to determine whether or not the arrangement for reducing the gas pressure to atmospheric is efficient enough to take care of any considerable variations in line pressure, and give a constant pressure at the meter inlet. The calorimeter was operated on gas from the holder till the reading became steady. The line pressure of the gas supplied was then varied from 2 to 8 incheq of water by increments of 2 inches, and the calorimeter mas allowed to operate for 45 minutes a t each increment. The pressure of the gas a t the inlet of the gas meter was measured by means of a n inclined water gage. h'o change was observed in the heating value recorded, as the pressure of the gas supplied varied from 2 to 8 inches of water. The readings taken on the inclined gage showed that the pressure a t the inlet to the gas meter was 0.003 inch water column and that it was the same for all line pressures between 2 and 8 inches of water column. Effect of Atmospheric Humidity
If the gas and the air delivered by the three meters operating in the tank of the Thomas calorimeter leave the meters completely saturated, humidity should have no effect on the readings. The humidity of the air in the room was varied from 29 to 88 per cent and the calorimeter operated throughout the test on gas from the holder, but no change in heating
A Vacuum Extractor for Biochemical Use'
Vol. 18, No. 10
value was recorded. This indicates that the gas and the air delivered by their respective meters are completely saturated. Performance
The first model tested a t the Chemical Engineering laboratories of the University of Wisconsin was installed in January, 1922, and was operated continuously over a period of 5 months. In February, 1923, a new model embodying certain changes was installed and the tests described in this paper were performed on the improved model. Since its installation, the improved model has been in operation for periods of time which total about 2 years and 2 months. A certain amount of routine attention and a few minor replacements have been necessary to keep the instrument in good condition. The tube for secondary air is subjected to extremely corrosive conditions from the products of combustion. It was found that this part, owing to failure from corrosion, had to be replaced approximately every 6 months. At the present time secondary air tubes of Pyrex glass are being tested to determine their suitability to replace the metal tubes now employed. The heat interchanger has suffered some on account of corrosion from the products of combustion, but it is still in use. The flexible metal hose connection from the gas pressure reducing chamber to the gas meter was replaced by a solid pipe connection. On all t h e new models the solid pipe connection is standard construction. The data obtained in these researches on several models submitted by the manufacturer have been factors in changes of design which have improved the precision obtainable.
With each of these solvents, a warm-water bath furnished sufficient heat for the extraction. The temperature of the
By N. B. Guerrant OKLAHOMA
AGRICULTURAL A U D MECHANICAL COLLEGE,
S T I L L W A T E R , OKLA
HE biological chemist is frequently confronted with the problem of extracting large quantities of material with various solvents. With the usual form of extraction apparatus the results are not always satisfactory, when the material is to be used in nutritional investigation. The accompanying diagram illustrates a piece of apparatus which has proved to be exceptionally useful in this type of work, especially where the effect of heat and oxidation is to be maintained at a minimum. The flask is of the thick-walled Pyrex balloon type, having 10 per cent greater capacity than the extraction chamber. The extraction chamber consists of a side-necked bell jar containing a perforated desiccator plate and covered with sb well-fitting desiccator top. The two ground surfaces are sealed with a mixture of equal parts of yaseline and paraffin previously melted and well mixed. The condenser should be shoit, thick-walled, and have a maximum cooling surface; the Davies condenser serves the purpose very satisfactorily. The exhaust tube should be as far as possible from the path of the condensed yapor. The valve, manometer, and the thermometer are optional. They are essential for accurate control of the apparatus. The valve is recommended where a water pump is used to produce the vacuum as the fluctuation of the water pressure may cause the water to be sucked back into the extraction chamber. This cannot happen where the valve is used. This apparatus has been used in the extraction of both animal and plant tissue with a number of solvents, among n hich were water, alcohol, acetone, gasoline, and ether. presented before the Dlvlsion of Blologlcal Chemistry a t the 71st nicetang of the ~ m e r i c a nChemical society, Tulsa, Okla , .4prl1 j to g 19% 1
boiling extract depends, of course, upon the degree of vacuum Obtained, but a pump> can be made with water without heating the extract abol e 65" c.
