STEAM-BATH. 97 



chance of firing the inflammable fluid or its vapour. In order to 

 economise the liquid, a series of tanks are generally arranged in 

 such a way that the liquid that runs from the first is made to pass 

 into the second, where it takes up more oil, and thence into the 

 third, and so on. 



Expt. 89. To separate the Fatty Matters from Milk. Cow's 

 milk is a very composite fluid, containing amongst other things 

 little globules of fatty matter floating about in a watery solution 

 of " milk sugar," " casein," and various other substances, somewhat 

 in the same way that vesicles of water float about in the air 

 forming mist or fog ; only the water vesicles are heavier than the 

 air, and so tend to settle down or sink, whilst the fat globules of 

 milk are lighter than the watery fluid, and so tend to rise and 

 float. Cream is simply the upper layer of milk, which becomes 

 much more heavily charged with fat globules on standing, owing 

 to this tendency to rise, whilst the lower layers become propor- 

 tionately poorer. 



Get a small saucepan full of boiling water, or better still the 

 copper hemispherical "water-bath," with rings of different sizes 

 to suit different sizes of basins, represented in 

 fig. 48 ; support this on a tripod, and place 

 on it an evaporating basin (fig. 35), so that the 

 basiii may be heated, not by direct flame, but 

 by the steam of the boiling water; this 

 arrangement is called a steam bath, and pre- 

 vents any possible burning of substances 

 placed in the basin. Pour into the basin half 

 a small wine-glassful of milk, and let the milk 

 evaporate slowly, stirring it now and then with 

 a bit of glass rod. By and by all the water Fi S- 48 ' Water Bath 



n T~ i if i -i i JTJ. .LI. an(i Rings- 



will be driven on, and a residue leit in the 



dish containing the fatty matters, caseine, milk sugar, &c., 

 originally contained in the milk. Let the dish cool completely, 

 and then pour on the residue two or three teaspoonfuls of 

 ether, and stir the whole up as much as possible. Now pour 

 off the ether into a second clean basin ; add more ether to the 

 residue, and stir up again ; and again pour off the ether into the 

 second basin. If this latter be now left exposed to the air for a 

 short time the ether will soon evaporate, and a film of fatty matter 

 will be left. Care must be taken that the ether does not fire 

 through its vapour coming in contact with a light (compare Expts. 

 41 and 88). If a little water be poured on the residue from 

 which ether has thus dissolved the fatty matter, it will in turn 

 dissolve out the milk sugar, which may be obtained in an impure 



G 



