LEFFMANX-BEAM METHOD. 225 



results : — Measure accurately 200 c.c. of acid into a large flask, 

 and to it add cautiously 15 c.c. of water, cooling the flask by 

 immersion in cold water. Take the specific gravity of this 

 diluted acid, either with, an accurate hydrometer or by other 

 means. If the temperature be not exactly 15'5° (60° F.), add on 

 O'OOl for each degree Centigrade above 15-5°, or 0'00056 for each 

 degree Fahrenheit above 60° F. (or subtract for temperatures 

 below). 

 The following table will give the strength of acid : — 



Specific Gravity of 

 Diluted Acid. 



1 -8.380, 

 1-8.349, 

 1-8311, 

 1 -8268, 

 1 8217, 



The figures in parentheses give the percentage of sulphuric 

 acid in the diluted acid, the other figures referring to the per- 

 centage of acid before dilution. 



Another method of determining the strength of acid is to 

 weigh about 1 gramme of acid in a basin and, after diluting 

 with water, to add an excess of strong ammonia. The solution 

 is evaporated on the water-bath and, when nearly dry, a little 

 more strong ammonia is added ; it is then dried to constant 

 weight at 100° C. (212° F.) and weighed. The weight divided 

 by 1-347 will give the weight of sulphuric acid in the sample; 

 this, divided by the weight taken and multiplied by 100, will 

 give the percentage. 



Purified amyl alcohol, free from petroleum, specific gravity 

 0-815 to 0-818 at 15-5° C. (60° F.), which completely dissolves 

 to a clear liquid when mixed with an equal bulk of hydrochloric 

 acid ; this mixture must not become darker than sherry in 

 three days. 



Commercial hydrochloric acid. 



The amyl alcohol is mixed with an equal bulk of hydrochloric 

 acid for use ; it is best not to keep this mixture longer than a 

 few days. 



The Process — Testing of Milk, Skim Milk, Buttermilk, 

 and Whey. — Measure 15 c.c. each of the well-mixed samples 

 into test bottles, holding the point of the pipette against the 

 side of the neck, so that the liquid may run down, allowing 

 room for the air to escape. Add 3 c.c. of the mixture of amyl 

 alcohol and hydrochloric acid. Pour in, -^vith care, 9 c.c. of 

 sulphuric acid, so that it washes down any particles of milk on 

 the neck of the bottle. Mix the contents of the bottle with a 

 rotatory motion ; a little practice is required to do this without 

 the liquid boiling over, owing to the heat evolved on mixing 



15 



