220 THE CHEMICAL CONTROL OF THE DAIRY. 



arrangement for keeping the water level constant in the bath is 

 necessary. 



After the dishes have been for about half an hour on the bath, 

 provided it has been boiling briskly, it will be noticed that a 

 distended skin has formed on the surface of the milk ; this must 

 be broken with a needle mounted in a handle, care being exer- 

 cised that no portion of the skin is brought away on the needle. 

 The object of this is to prevent the milk drying in flakes, which 

 may be blown away by draughts, and the estimation lost. Should 

 the dishes be forgotten, or should any other reason prevent 

 the stirring being done at the proper moment, a few drops of 

 water may be added to the milk residue, which will have the 

 efiect of making the flakes settle down and adhere to the dish. 

 When the dishes have been on the water-bath for three hours, 

 they should be taken ofi, placed on a tray having two or three 

 thicknesses of blotting-paper on the bottom to remove adhering 

 drops of water, and transferred to a water-oven or air-bath. 

 The important point about the water-oven is that it has an even 

 draught passing through it ; the form of air-bath devised by 

 Dr. Adams of Maidstone is suitable, though the cover is a little 

 troublesome to remove. The dishes are placed upon wire 

 shelves one above the other, and it is convenient to have ten or 

 twenty dishes on each shelf. If a good draught be maintained 

 in the water-oven or air-bath, it is not necessary or advisable to 

 keep this at a higher temperature than 90° to 95° C. After three 

 hours drying in the air-bath, the dishes should be weighed. 



Weighing. — Ten basins (or any number that can be con- 

 veniently placed in the balance case at one time) should b'e 

 removed from the bath, placed on a tray and conveyed to a 

 desiccator, and there allowed to cool for a few minutes. Plati- 

 num basins cool very much faster than porcelain, and much 

 time is saved by their use ; when cool, they should be weighed 

 to the nearest miUigramme, the weight entered in the book 

 opposite to the number of the dish; the weight of the empty 

 dish (from the table of weights) should be subtracted, and the 

 weight of the milk residue will be the difference between the 

 two weights ; this also should be entered in the book. As 

 5 grammes of milk were taken, the residue, multiplied by 20, 

 will give the percentage of total solids in the milk. 



If the samples arrive in the laboratory in sample bottles and 

 not in cans, a somewhat different mode of procedure must be 

 adopted. A number of cylindrical tins without lids (of such a 

 size as to hold the contents of a sample bottle) and a lactometer 

 are necessary. The bottles and dishes are arranged in their 

 proper order and entered in the book, as before. As many 

 bottles as there are tins are shaken, to mix the cream, and emptied 



