CHEMICAL TESTS AND ANALYSES 343 



one and one-half inches wide. Fill the cylinder with milk at a 

 temperature between 55 and 65 degrees F. Insert the lactometer 

 and when it has found its equilibrium, note the point on the scale_ 

 at the surface of the milk. The correct temperature is 60 degrees 

 F. For every degree Fahrenheit -above 60 add one-tenth point 

 to the observed reading, and for every degree Fahrenheit below 

 60 deduct one-tenth point from the observed reading. This rule 

 holds good only when the range of temperature is within the 

 limits of 55 degrees and 65 degrees F. 



The specific gravity is calculated by adding 1,000 to the 

 lactometer reading and dividing the sum by 1,000. Example: 

 Lactometer reading is 31 at 65 degrees F. Corrected reading is 

 31.5; 



. . 31.5 4- 1000 1 _, 

 specific gravity is ' : 1.031X 



Gravimetric Determination. This consists of the filling of 

 a perfectly dry picnometer or other graduated flask of known meas- 

 ure with milk at the standard temperature (60 degrees F., or 15.5 

 degrees C.) and weighing the flask and contents. The weight of 

 the flask is then deducted from the weight of the flask plus con- 

 tents and the difference is divided by the weight of an equal volume 

 of water at standard temperature. The result is the specific gravity 

 of the milk. 



The Westphal balance method furnishes another accurate means 

 of determining the specific gravity. Both the gravimetric method 

 and the Westphal balance method, while accurate when operated 

 by the skillful chemist, require considerable time. Experimental 

 comparisons have demonstrated that for all practical purposes the 

 Quevenne hydrometer, when accurately graduated, yields correct 

 results, and the simplicity and rapidity of its operation render its 

 use in the determination of the specific gravity of milk highly ad- 

 vantageous and satisfactory. 



Total Solids. 



By Means of the Babcock Formula. For rapid and reason- 

 ably accurate work the total solids of milk may be determined by 

 the use of the Babcock formula, which is as follows : 



Total solids =-^-+ 1.2 X f. 



