EGGS OF FOWLS. 449 



Chevreul has found two colouring matters in the yolk, the one 

 red, and the other yellow. 



Lecanu, besides the stearin and elain, extracted from the yolk 

 of egg a crystalline matter which melted at 293, and which he 

 considered as of the same nature with cholesterin from the brain.* 



Dr Proutf determined the quantity of fixed constituents of 

 dried yolk of egg by incineration. He pounded the yolk with 

 bicarbonate of potash in a mortar, and then heated it in a cover- 

 ed platinum crucible till flame ceased to escape from a small 

 hole in the lid. The contents when cold were removed from the 

 crucible and again pounded with nitre. The mixture was now 

 introduced by a little at a time till the whole was burnt. To the 

 residuum water was added, which dissolved every thing but the 

 earthy phosphates. From the aqueous solution everything was 

 obtained except the alkaline matter contained in the yolk. To 

 obtain these a new portion of the yolk was treated as before, sub- 

 stituting lime and nitrate of lime for bicarbonate of potash and 

 nitre. The following table exhibits the quantity of fixed matter 

 obtained in this way from three different yolks : 



No. 1. No. 2. No. 3. 



Sulphuric acid, . . 0-21 0-06 0-19 



Phosphoric acid, . . . 3-56 3-50 4-00 



Chlorine, . . . 0-39 0-28 0-44 



Potash, soda, and carbonates of do. 0*50 0-27 0*51 

 Lime, magnesia, and carbonates of do. O68 0-61 0'67 



5-34 4-72 5-81 



Whether the sulphur and phosphorus exist in the yolk in the 

 state of acids, or as sulphur and phosphorus is not known, though 

 the last supposition is most probable. When we compare the 

 fixed constituents of the white and yolk, we cannot avoid being 

 struck with the difference. The white contains a much greater 

 quantity of fixed alkalies than of any other fixed constituent ; 

 while in the yolk the most abundant constituent is phosphoric 

 acid, which amounts to from 3*5 to 4 grains, or, if we suppose it 

 to exist, as phosphorus, it varies in a single yolk from 1*55 to 

 1*77 grains. 

 The specific gravity of a new laid egg varies from 1*080 to 



* Berzelius, Traite de Chiraie, ix. 573. f Phil. Trans. 1822, p. 386. 



Ff 



