318 Change of Fat in Perkhis's Engine, by Water, Heat, Sfc. 



pable of exhibiting this change; one of them was of a 

 sHght violet tint, the other two purple or pinkish, but the tint 

 scarcely perceptible except by looking at the edges. They 

 were each brokeni nto two pieces ; three of the pieces were 

 then wrapped up in paper and set aside in a dark place, and 

 the corresponding pieces were exposed to air and sunshine. 

 This was done in .January last, and the middle of this month 

 (September) they were examined. The pieces that were put 

 away from light seemed to have undergone no change ; those 

 that were exposed to the sunbeams had increased in colour 

 considerably ; the two paler ones the most, and that to such a 

 degree, that it would hardly have been supposed they had 

 once formed part of the same pieces of glass as those which 

 had been set aside. Thus it appears that the sun's rays can 

 exert chemical power's even on such a compact body and per- 

 manent compound as glass." 



CHANGE OF FAT IN PERKINS's ENGINE BY WATER, HEAT, AND 

 PRESSURE. 



Mr. Perkins uses in his steam cylinder a mixture of about 

 equal parts of Russia tallow and olive oil to lubricate the piston 

 and diminish friction. This mixture is consequently exposed 

 to the action of steam at considerable pressure and tempera- 

 ture, and being carried on by the steam, it is found in the 

 water, giving rise to peculiar ajipearances. The following is 

 Mr. Faraday's account of it. 



The original mixture is solid at common temperatures, but 

 fuses at about 85° Fah. When boiled in alcohol, a small 

 portion dissolves. 



The water, as it issues from the end of the ejection-jiipe into 

 the tub placed to receive it, and from which it is pumped up 

 again into the generator, appears white and translucent, and 

 after having been used some time, very much resembles thin 

 milk. A scum is found floating on it, which, when collected 

 together, forms a soft solid, but when it has been long ex- 

 posed to the action of the steam and at a high temperature, is 

 hard like wax nearly. It is always black and dirty. A portion 

 of this substance was digested in hot alcohol, and the clear 

 solution set aside ; flocculi separated in abundance from it on 

 cooling, which, when dried, collected, and fused, gave a grayish 

 substance, contracting and cracking as it cooled, with the 

 lustre and appearr.nce of wax, but rather more binttle. It 

 does not melt in boiling water, but at a higher heat melts, and 

 ultimately burns like fat. It is rather lighter than water ; it 

 dissolves readily in alkalies, more readily, I think, than fat, 

 and in this respect resembles Chevreul's acids of fat, as well 



