SPECIAL REACTIONS 71 



1. Pour some 2 per cent, grape sugar bouillon, made just before 

 using, into the bulb of the tube until it is half full. 



2. Tilt the tube until the closed arm is nearly horizontal, so that 

 the air in the arm may escape into the bulb and the fluid flow into 

 the arm to take its place. 



3. When the arm is completely filled, add enough of the liquid 

 medium to cover the lowest expanded portion of the bulb, and close 

 the opening of the bulb with cotton wadding. 



4. Sterilize the tubes on three consecutive days by the usual 

 method. 



During the process of sterilization the tension of the water vapour 

 in the arm forces most of the fluid into the bulb. When the tube 

 cools, the fluid returns again into the arm, except in a small space at 

 the top, occupied by air originally dissolved in the liquid, and which 

 was driven out by the heat. The air bubble must be tilted out after 

 each sterilization, and finally after the third sterilization the arm of 

 the tube will be free from air. 



After inoculation, the tubes are placed in the incubator, and the 

 amount of gas collecting in the closed arm noted daily. The gas is 

 usually found to consist of about one part by volume of carbonic acid 

 and two parts by volume of an explosive gas, consisting largely of 

 hydrogen. 



CXXXI. METHOD OF DETERMINING THE NATURE 

 AND QUANTITATIVE RELATIONS OF THESE 

 GASES ACCORDING TO SMITH. 



The bulb is completely filled with a % per cent, solution of 

 sodium hydroxide (NaOH), and closed tightly with the thumb. 

 The fluid is thoroughly shaken with the gas, and allowed to flow to. 

 and fro from bulb to closed branch several times to insure intimate 

 contact of the CO 2 with the alkali. Lastly, before removing 1 the 

 thumb all the gas is allowed to collect in the closed branch, so that none 

 may escape when the thumb is removed. If CO 2 is present, a partial 

 vacuum in the closed branch causes the fluid to rise suddenly when 

 the thumb is removed. After allowing the layer of foam to subside 

 somewhat, the space occupied by gas is again measured, and the 

 difference between this amount and that measured before shaking 

 with the sodium hydroxide solution gives the proportion of CO 2 

 absorbed. 



CXXXII. Determine the explosive character of the residue as 

 follows : 



