104 POODS AND FOOD ADULTERANTS. 



1mm.) ; the stem is about 23cm., and the Lull* about 8cm. long. It is important that the 

 shoulder bet WOOD the stem and the bulb should not be loo abrupt. The bore of the stem 

 is about 6mm., and it is graduated in ^cc. The wider part of the tube has such a capac- 

 ity that in passing from the lowest graduation on the stem to the inner end of the 

 stopper in the lower mouth one passes from 5 to 33cc. ; then the ether-fat solution will 

 always come within the range of tlio graduation on the stem. This instrument differs 

 from that originally given by Marchand only in being open at the bottom as well 

 as at the top ; this is a matter of some importance with reference to cleaning and 

 drying it. The narrow stem in which the ether-fat solution collects makes more 

 accurate readings possible than is the case with the wider tube with the same width 

 of bore throughout, such as is now commonly used. 



The manipulation is carried on as follows : 



Closing the lower mouth with a good cork, lOcc. of the well-mixed sample of milk 

 are delivered into the well-dried tube from a pipette, Mien 8cc. of ether (Squibbs's 

 stronger) and 2cc. of 80 per cent, alcohol. Close the smaller mouth of the tube with a 

 cork, and mix the liquids by thorough shaking, which, however, need not be either 

 violent or prolonged. Both corks should be held in place by the lingers during this 

 operation, and the upper one should be once or twice carefully removed to relieve 

 the pressure within, otherwise it is liable to bo forced out suddenly unless carefully 

 watched, with consequent danger of loss of material. Lay the tube on its side for a 

 few minutes and then shake it again, add Ice. of ordinary ammonia diluted with about 

 its volume of water, and mix as before by shaking ; then add lOcc. of 80 per cent, 

 alcohol, and mix again thoroughly by moderate shaking, and holding the tube from 

 time to time in an inverted position while the lighter portion of the liquid rises to 

 the surface. 



Now put the tube in water kept at 40 to 45 C. till the ether-fat solution separates- 

 this separation may be hastened by transferring the tube to cold water after it has 

 stood in the warm water for a few minutes and then returning it to the warm water. 

 Finally transfer the tube to water kept at 'about 20 C., and as the level of the liquid 

 falls in the stem by the contraction of the main body of it in the bulb, gently tap the 

 side of the tube below the ether-fat solution, to dislodge any flakes of solid matter 

 that may adhere to the walls ; then as this solution finally takes its permanent posi- 

 tion in the tube, its volume will not be increased by the presence of such foreign 

 matters. The readings are to be taken from the lowest part of the surface meniscus 

 to the line of separation between the ether-fat solution and the liquid below it. 



Iii this laboratory the use of the lactobutyrometer has been attended 

 with the same difficulties, though to a less extent, which led to the modifi- 

 cation of Soxhlet's method already noticed. The late improvements in 

 both the volumetric and gravimetric determinations of fat in milk ren- 

 der a further discussion of the merits of the lactobutyrometer unnec- 

 essary. 



OPTICAL METHODS OF ESTIMATING FAT IN MILK. 



Since the white color of milk is due to the suspension of the fat glob- 

 ules, many devices have been contrived to determine the quantity of fat 

 present by the opacity of the milk. The most convenient of these ap- 

 paratus is the one designed by Feser. 



It consists of a glass cylinder, in the lower part of which a smaller 

 cylinder made of white glass is fixed. On this white glass arc a few 

 black lines. The outer cylinder carries a double scale, one set of num- 

 bers representing cubic centimeters and the other the percentage of fat. 



