WEIGHING. 105 



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 desiccator at one time) should be 

 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 milligramme, 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, 

 would 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 

 into the tins ; 5 grammes are taken from each and placed in 

 the dishes, but before the milk is poured back into the bottle 

 or otherwise emptied from the tin, the temperature and specific 

 gravity should be taken ; the remaining samples are then treated 

 similarly in their proper order. The drying and weighing are 

 performed as before. 



Rapid Methods. A pipette is used which delivers 2-5 

 grammes of milk, and the milk is run into flat-bottomed por- 

 celain basins about 3 inches in diameter. The numbers are 

 marked on the basins with copper paint, which paint, on ignition, 

 forms an indelible blue mark. Before the basins are filled, 

 Stokes recommends that two or three drops of a 10 per cent, 

 solution of acetic acid in alcohol be sprinkled over each. The 

 alcohol spreads itself over the surface of the milk, and the acid 

 precipitates the casein. Revis adds 1 c.c. of acetone. Under 

 these circumstances, drying proceeds very rapidly. The basins 

 are placed on the water-bath till apparently dry, a matter of 



