186 



MODERN METHODS OF TESTING MILK 



shows a lactometer reading of 32. What 

 is the per cent, (a) of solids-not-fat, (b) 

 of total solids? 



(a) The lactometer reading (32), di- 

 vided by 4, equals 8. The per cent, of 

 fat (4), multiplied by .2, equals .8. Add- 

 ing 8 and .8, we obtain 8.8 as the per 

 cent, of solids-not-fat. 



b) The per cent, of total solids in the 

 milk is 12.8 per cent.; for the lactometer 

 reading, divided by 4, equals 8, the per 

 cent, of fat (4) multiplied by 1.2 equals 

 4.8, and 8 plus 4.8 equals 12.8. 



Richmond's slide-rule for calculating 

 solids. Instead of going through the 

 details of calculation to estimate solids 

 in milk, Richmond uses a slide-rule which 

 is a clever mechanical calculating device. 

 (Fig. 51). The results obtained in this 

 manner agree closely with those given by 

 Babcock's formulas. The method of 

 using the slide-rule is as follows: De- 

 termine (i) the Quevenne lactometer 

 reading, (2) the temperature of the 

 milk, and (3) the per cent, of fat in the 

 milk. Then set the central slide of the 

 rule so that the observed lactometer read- 

 ing is opposite the 60 degree (tempera- 

 ture) mark. The true lactometer read- 

 ing is found opposite the line indicating 

 the observed temperature of the milk. Having thus 

 corrected the lactometer reading for temperatures 



FIG. 50 

 RICHMOND'S 



SLIDE-RULE 



