216 THE CHEMICAL CONTROL OP THE DAIRY. 



for testing in the dairy than in the laboratory, where samples 

 are often limited. It has, however, the advantage of not re- 

 quiring a separate thermometer and a separate operation to 

 determine the temperature. 



Vieth's lactometer (Fig. 19) may be used in a can and, if the 

 samples are received in cans, as is often the case in a dairy labora- 

 tory, no transference of the sample is necessary. 



Soxhlet's lactometer has a wider scale, and may be conveni- 

 ently used when greater accuracy is required. 



Galaine's self-correcting lactometer has a metal ball com- 

 pletely filled with chloroform attached to the bottom, the object 

 being to obviate the necessity of correction of the specific gravity 

 for temperature ; the expansion of the chloroform was supposed 

 to compensate the expansion of the milk. Though excellent in 

 theory, it has proved disappointing in practice. 



Beam's lactometer is devised to obviate the difficulty of 

 determining the exact point where the surface of the milk cuts 

 the stem. It consists of a specially graduated lactometer and 

 a float, and the reading is made by observing the point on the 

 stem which corresponds with the uppermost portion of the glass 

 tube of the float. 



In use, it is essential that the stem remain dry. Beam's 

 directions for use are : — The stem of the lactometer being dry 

 the float is passed over it and allowed to rest on the bulb. The 

 lactometer is then lifted by the point of the stem, and gradually 

 let into the milk. If there is any doubt as to the instrument 

 having found its proper level, the base of the jar may be held 

 firmly to the table by one hand and the jar gently tapped with 

 the other. 



When removing the lactometer the float should be taken out 

 first, in order to keep the tube dry and- ready for another test. 



The following directions are due to Vieth : — 



Use of Lactometer. — In order to determine the specific 

 gravity, the milk is poured into a vessel at least ^ inch greater 

 in diameter than the widest part of the lactometer, and deep 

 enough to allow the instrument to float. A cylindrical glass 

 jar (Fig. 20), with foot, is the most suitable vessel for the pur- 

 pose if Soxhlet's lactometer or the thermo-lactometer be used; 

 Vieth's lactometer may be used in a can or tin cup. The lacto- 

 meter is gradually lowered into the milk to the 25th degree, 

 care being taken that the instrument is entirely wetted by the 

 milk and that no air adheres to it. When released, the lacto- 

 meter will move up and down, and after a little while become 

 stationary. That degree of the scale which coincides with the 

 surface of the milk is then noted. It will be observed that, 

 where the milk touches the vessel and the stem of the lactometer, 



