134 SOIL BACTERIOLOGY 



(3) Methyl-red: 



Methyl-red 2 gm. 



Alcohol (95 per cent.) 1000 c.c. 



Dissolve the methyl-red in alcohol and filter. 



(4) Cochineal: 



Cochineal (pulverized) 6 gm. 



Alcohol (95 per cent.) 50 c.c. 



Distilled water. . . . 200 c.c. 



Shake the cochineal in the mixture of water and alcohol. 

 Allow to stand for two days at room temperature. Filter 

 until clear. The color of this solution should be a deep 

 ruby red ; in the presence of alkali a violet color, and in the 

 presence of acid a yellowish-red color. 



(5) Preparation of Standard Solution of Sulphuric Acid. 

 A normal solution of sulphuric acid is one-half the molecular 

 weight of H 2 SO 4 in grams, diluted to i liter with distilled 

 water. Since the molecular weight of sulphuric acid is 

 (2+32+64) 98, then 49 grams, one-half of 98, is the amount 

 necessary for each liter. 



1. In order to secure 49 grams of H 2 SO4, it requires 49 

 divided by 1.80, or 27.2 c.c. of chemically pure acid. To 

 be sure that sufficient acid has been used, measure out 

 about 27.5 c.c. of acid. 



2. Place in looo-c.c. graduated flask, make up to 1000 

 c.c., and mix carefully. 



3. From this mixture remove lo-c.c. portions, accurately 

 measured in a ic-c.c. pipet, and place in weighing bottles 

 which have been thoroughly cleaned, dried in an oven, 

 cooled, and weighed. 



