THE RESPIRATION APPARATUS. 33 



the S. S. White Dental Manufacturing Company, of Philadelphia. 

 This oxygen has been in use for some years in this laboratory in con- 

 nection with the bomb calorimeter 1 and the carbon and hydrogen 

 determinations. 2 



It contains, besides oxygen, from 2.5 to 8 per cent of nitrogen and 

 small quantities of carbon dioxide and water vapor, but no appreciable 

 quantities of hydrogen or gaseous hydrocarbons. In preparing it for 

 use it is necessary only to remove the carbon dioxide and water and 

 determine quantitatively the percentage of nitrogen. 



The oxygen is contained in steel bottles or cylinders (fig. 15) 61 cm. 

 high, ii cm. in diameter, weighing (exclusive of purifying apparatus), 

 when charged with 283 liters of oxygen at a pressure of 2,000 pounds 

 to the square inch, about 7 kg. 



A metal yoke is securely fastened to the valve with a screw clamp 

 and leather washer, and a brass T tube conducts the oxygen into a 

 rubber gas-bag 3 and through the side outlet to the purifying device. 

 The use of the bag is imperative, for the pressure in the cylinder is so 

 high that however carefully the valve is opened the gas escapes so sud- 

 denly that the connections are liable to be disturbed unless an overflow 

 for the surplus gas is provided. 



The gas then enters a large U tube fastened to the side of the cylin- 

 der by means of two rubber bands. The U tube is filled with soda 

 lime, such as is used in the carbon-dioxide absorbers in the main system. 

 To prevent any particles of soda lime from being carried mechanically 

 out of the U tube, a tuft of cotton batting is placed at the exit end. 

 In its passage through the soda lime the gas is completely freed from 

 carbon dioxide. It still retains the moisture it originally contained, 

 and some that it has taken from the moist soda lime. To remove the 

 moisture, the gas is next passed through a drying tube of special con- 

 struction, filled with pumice stone drenched with sulphuric acid. A 

 bulb at the lower end allows for the accumulation of spent acid. By 

 an actual test it has been found that such a tube will remove all the 

 water vapor from the oxygen in at least ten cylinders before it needs 

 refilling. 



As a matter of fact, when the bulb at the lower end becomes filled 

 with spent acid, the tube is removed, inclined so as to drain out the 



1 Jour. Am. Chem. Soc. (1903), 25, p. 569. 



2 Benedict, Elementary Organic Analysis, p. 4. 



3 The bags are made for us by the Davol Rubber Company, of Providence, Rhode 

 Island. They are extra heavy wall, of pure rubber, and will withstand considerable 

 tension without noticeable leak. It is estimated that a bag 21 cm. long (measured, 

 when folded) will, as a rule, readily take care of 2 or 3 liters of oxygen without 

 loss. It is seldom, however, that an excessive amount of gas enters the bag, as the 

 adjustment can usually be readily made by means of the valve. 



3B 



