

PRODUCTS. 105 



Four cubic centimeters of milk are put in the cylinder and then water 

 added until the black lines on the inner white cylinder become visible. 

 The percentage of fat is then read from the top of the column of water 

 in the large cylinder. 



For a full description of the different forms of lactoscope the mon- 

 ograph of von der Becke may be consulted. 1 For sorting milks, the 

 lactoscope in the hands of an experienced operator will give valuable 

 indications in respect of the quantity of fat. A delicate lactometer, a 

 good lactoscope, and an experienced operator will generally be able to 

 determine whether a given sample of milk be whole or skimmed. The 

 lactoscope, however, is of no value in determining with accuracy the 

 percentage of fat present in a sample of milk. 



ESTIMATION OF LACTOSE. 



Chemical. The chemical methods employed in estimating the sugar 

 in milk will be fully discussed in another part of this bulletin devoted 

 to the study of sugars and their adulterations. 



Optical. The optical method of determining the quantity of lactose 

 in milk is both speedy and accurate when properly carried out. The 

 principles which underlie this investigation and the proper method of 

 carrying it out are given below. 2 



The usual method of determining rnilk sugar by evaporating the sam- 

 ple to dryness and extracting the sugar with alcohol after exhausting 

 with ether requires a great deal of time and labor. If some reliable 

 optical method could bo devised the determination of the lactose in 

 milk would be the work of only a few minutes. The difficulties which 

 are encountered in seeking for such a method are numerous and serious, 

 so much so that little credit has heretofore been given to any of the 

 processes of optical analysis in use. 



SPECIFIC ROTATORY POWER OF MILK SUGAR. 



Crystallized milk sugar when first dissolved possesses a higher rotatory 

 power than it has in the milk from which it was derived. This increased 

 optical activity may be compared with the original by the ratio 8 : 5, 

 nearly. After the solution has stood for twelve to twenty hours, or im- 

 mediately on boiling it, this extra rotatory power is lost. In estimating 

 the specific rotatory power of milk sugar the numbers given always refer 

 to the constant and not the transient gyratory property. 



Among the earliest numbers assi gned to the rotation of lactose are those 

 of Poggiale (a) n = 54.2 and Erdmauri () u = 51.5 [Sucrose (a) H = 66.5]. 

 Biot 3 places this number for lactose at G0.23, and Berthelot 4 at 59.3 for 

 the transition tint ()_,. Hoppe-Seyler, in his "Handbuch der physiolo- 

 gisch-chemischen Analyse," gives this number at (a)j=58.2. Since the 



1 Op. cit., pp. 45 et Hcq. 2 Am. Chein. Jour., vol. 6, pp. 289 ct scq. 



3 Compt. Rend., vol. 42, p. 349. ' Wiirt/ Diet, do Chim., vol. 2, 1st part, p. 188. 



