DAIRY PRODUCTS. 45 



form of a small hook, is dipped into the melted fat, a portion of which 

 adheres to it. This process is repeated until a sufficient insulation is pro 

 duced. The fat-covered end of the wire is then dipped into a mercury 

 cup, which contains also the bulb of the thermometer. The cup is placed 

 .in the electric circuit and the moment of contact is determined by the 

 ringing of an electric bell. Thorough trial of this method convinced me 

 that it was less accurate than any of those which have already been 

 mentioned. 



Bealiziug the importance of determining some definite point at which 

 fats would assume a constant condition under the influence of tempera- 

 ture, I was led to select another physical aspect of fats, easily and cer- 

 tainly visible, which could be regarded as the melting point. This con- 

 dition may be defined as the point at which the molecular attraction of 

 the fat becomes greater than the molecular cohesion. 



If a thin film of any fat be suspended in a liquid of equal specific 

 gravity with it and this liquid be slowly warmed, a point will be reached 

 at which the film will roll up and finally assume the form of a sphere. 

 By imparting to the globule a gentle motion of rotation the observer is 

 easily able to distinguish the moment when it becomes sensibly sym- 

 metrical. I use the following method and apparatus for applying this 

 principle to the determination of the melting points of fats. 1 The ap 

 paratus consists of (1) an accurate thermometer for reading easily tenths 

 of a degree; (2) a less accurate thermometer for measuring the -tem- 

 perature of water in the large beaker glass ; (3) a tall beaker glass, 

 35cm. high and 10cm. in diameter; (4) a test tube 30cm. high and 3.5cm. 

 in diameter; (5) a stand for supporting the apparatus; (6) some method 

 of stirring the water in the beaker. I use a blowing bulb of rubber and 

 a bent glass tube extending to near the bottom of the beaker ; (7) a 

 mixture of alcohol and water of the same specific gravity as the fat to 

 be examined. 



Manipulation. The disks of the fat are prepared as follows : The 

 melted and filtered fat is allowed to fall from a dropping tube from a 

 height of 15 to 20cm. onto a smooth piece of ice floating in water. The 

 disks thus formed are from 1 to IJcm. in diameter and weigh about 200 

 milligrams. By pressing the ice under the water the disks are made 

 to float on the surface, whence they are easily removed with a steel 

 spatula, 



The mixture of alcohol and water is prepared by boiling distilled 

 water and 95 per cent, alcohol for ten minutes to remove the gases 

 which they may hold in solution. While still hot the water is poured 

 into the test-tube already described until it is nearly half full. The test 

 tube is then filled with the hot alcohol. It should be poured in gently 

 down the side of the inclined tube to avoid too much mixing. If the 

 tube is not filled until the water has cooled the mixture will contain so 

 many air bubbles as to be unfit for use. These bubbles will gather on 

 Journal Anal. Chemistry, vol. 1, No. 1, pp. 39 et seq. 



