MATHEMATICS AND NATURAL PHILOSOPHY. 449 



producing grape sugar. Tannin, when thus treated, readily gives oxalic acid, and 

 a yellowish amorphous substance, like gum arabic, having the same composition 

 as cane sugar but none of its reducing power. No trace of sugar is formed during 

 this reaction. 



STRYCHNINE. 



Prollius proposes a method for separating strychnine, which promises to be of 

 considerable value in toxicological investigations. The substance is digested with 

 alcohol and a little tartaric acid, gently evaporated to a small bulk, and filtered to 

 separate the fat. (If evaporated to dryness the fat might be separated by ether, 

 which does not dissolve salts of the alkaloids.) To the filtrate ammonia is 

 added, then a small quantity of chloroform, and the whole strongly agitated. The 

 chloroform, which settles to the bottom, is drawn off and washed, mixed with 

 three times its bulk of alcohol, and allowed to evaporate. Fine crystals of strych- 

 nine are thus obtained in a state of absolute purity. 



H. C. 



MATHEMATICS AND NATURAL PHILOSOPHY. 



THE RELATIONS OF GOLD TO LIGHT. 



At a meeting of the Royal Institution, in June last, Professor Faraday read a 

 communication on the relation of gold to light. In this he furnished additional 

 views and observations of great interest, in continuation of a former paper on the 

 same subject, read by him last year, and printed in the Proceedings of the Royal 

 Institution (Vol. II. p. 310.) The general relations of gold leaf to light are de- 

 scribed in the former communication. The following is a summary of the addi- 

 tional remarks which complete the report of Professor Faraday's observations on 

 the subject up to this time : — Since the printing of the former paper pure gold 

 leaf has been obtained, through the kindness of Mr. Smirke, and the former 

 observations verified. This was the more important in regard to the effect of 

 heat in taking away the green colour of the transmitted light, and destroying to a 

 large extent the power of reflection. The temperature of boiling oil, if continued 

 long enough, is sufficient for this effect ; but a higher temperature (far short of 

 fusion) produces it more rapidly. Whether it is the result of a mere breaking up 

 by retraction of a corrugated film, or an allotropic change, is uncertain. Pressure 

 restores the green colour, but it also has the like effect upon films obtained by 

 other processes than beating. Corresponding results are produced with other 

 metals. As before stated, films of gold may be obtained on a weak solution of 

 the metal, by bringing an atmosphere containing vapours of phosphorous into 

 contact with it. They are produced also when small particles of phosphorous are 

 placed floating on such a solution ; and then, as a film differing in thickness is 

 formed, the concentric rings due to Newton's thin plates are produced. These 

 films transmit light of various colours. Wheu heated they become amethystine 

 or ruby, and then when pressed become green, just as heated gold leaf. This 

 effect of pressure is characteristic of metallic gold, whether it is in leaf, or film, 

 or dust. Gold wire, separated into very fine particles by the electric deflagration, 

 produces a deposit on glass, which, being examined, either chemically or physi- 



