44 



MODERN METHODS OF TESTING MILK 



of acid, the exact quantity being determined by trying 

 different amounts of acid, until the fat-column obtained 

 is clear and yellow. Strong acid, if allowed to stand 

 open to the air, will in time absorb 

 enough moisture to reduce it to proper 

 strength. By far the best plan is to 

 purchase the acid of guaranteed spe- 

 cific gravity 1.82 to 1.83, since all 

 dairy-supply houses now furnish such 

 acid, and then take pains to keep the 

 acid in tightly stoppered bottles when 

 not in use. 



Testing strength of acid. The 

 strength of sulphuric acid may be con- 

 veniently tested by a specially designed 

 hydrometer (Fig 18). This instru- 

 ment or acidometer is simply allowed 

 to float in the sulphuric acid, which 

 must be at 60 F., and the specific 

 gravity is read from the scale where 

 it coincides with the upper surface of 

 the liquid, which should be between 

 the scale-marks 1.82 and 1.83. No 

 acidometer should be used whose ac- 

 curacy is not reliably guaranteed. ACID 



Reducing the strength of strong acid. With the 

 aid of an acidometer, it is possible to purchase strong 

 sulphuric acid and dilute it to proper strength. This 

 is not advised for the average worker. When this is 

 done, extreme caution must be used in diluting the 

 acid. Never pour water into strong sulphuric acid, 

 but always add the acid to the water. The amount of 



FIG. 1 8 



HYDROMETER FOR 

 TESTING STRENGTH 



OF SULPHURIC 



