64 Testing Milk and Its Products. 



the ammonia must, however, be applied while the stain 

 is fresh, and is in its turn washed off with water. 



73. Testing the strength of the acid. The strength of 

 the acid can be easily tested by the use of such a balance 

 as shown in Fig. 33 (94). A dry test bottle is weighed, 

 and then filled with acid exactly to the zero mark, or to 

 any other particular line of the scale. It is then again 

 weighed accurately; the difference between these two 

 weights will give the weight of the acid in the bottle. 

 Next empty the bottle and rinse it thoroughly with water 

 (until the water has no longer an acid taste); fill the 

 bottle with water to the same line as before and weigh ; 

 the difference between this weight and that of the empty 

 bottle gives the weight of the same volume of water as 

 that of the acid weighed. Divide the weight of the acid 

 by the weight of the water; the quotient gives the spe- 

 cific gravity of the acid. If this is between 1.82 and 

 1.83, the strength of the acid is correct. The outside of 

 the test bottle should always be wiped dry before the 

 liquids are weighed in it. Unless great care is taken in 

 measuring out the acid and the water, and in weighing 

 both these and the test bottle, the results obtained will 

 not be trustworthy. 



74. Too strong acid can sometimes be successfully used 

 by taking less than the required amount of each test, e. g. 

 about 15 cc. Operators are warned against reducing the 

 strength of the acid by adding water to it, as accidents 

 are very apt to occur when this is done. A too strong 

 acid can, if desired, be weakened by simply leaving the 

 bottle which holds it, uncorked for a time, or by pouring 

 the acid into a bottle containing a small quantity of 



