i MILK 25 



is cither fixed to the lower wider part of the lactometer or else 

 in an extension of the stem. 



In France and Switzerland, Quevenne's lactometer is largely 

 used, and it also is sometimes provided with a thermometer. 

 The scale of Quevenne's lactometer has more divisions than 

 Soxhlet's, so the space between two divisions is less, and the 

 difficulty of taking a very accurate reading is greater. 



There are many different sorts of lactometers to be bought, 

 only few of which, however, are really reliable. Great care 

 should be exercised when buying a lactometer to get an 

 accurately-adjusted instrument. 



When making a determination of the specific gravity of milk, 

 it is not essential to have the temperature exactly at 15 C. 

 It is sufficient if it lies between 10 and 20 C., for with the 

 help of the table drawn up by Chr. Mtiller (Table I in Appendix) 

 the specific gravity obtained at temperatures between these 

 two can easily be calculated to 15 C. 



The milk which is to be tested should be well mixed and 

 enough poured into a glass cylinder, which must not be too 

 narrow, to fill it two-thirds full. If this is done carefully, then 

 no foam will be formed on the surface, but should there be any 

 it must be removed in some suitable way, e.g. by filter paper. 

 The lactometer, which must be clean and dry, is held by the 

 stem and carefully lowered into the milk until the surface 

 of the liquid is at division 30 on the scale (T030). It is then 

 freed, and when it has come to rest the height of the milk on 

 the scale is read off, care being taken to have the eye on the 

 same level as the surface of the milk. Around the stem of the 

 lactometer the level of the milk is slightly raised owing to 

 adhesion. This must be allowed for in the reading ; as a rule 

 it is about T Vth of a degree. If, for instance, 30*2 has been read 

 off on the scale, then 0*1 must be added, making 30'3 (1'0303). 



Each time after it has been used, the lactometer must be 

 washed under the water-tap and then carefully dried, for if it is 

 left unwashed the milk will dry on to the glass and be difficult 

 to get off. 



For very accurate determinations, as in scientific investiga- 

 tions, it is safer to use a pyknometer or a Westphal balance. 

 The construction of these instruments and the method of using 

 them are well known to chemists, so will not be dwelt upon 



