M. C. Deville on the origin of Granite. 175 



and weak spirit of wine all contain the same combustible sub- 

 stances, — carbon and hydrogen ; yet the envelope of the flame 

 of a candle is bright yellow, that of a coal-gas flame is purple, 

 and those of strong and weak spirit differ greatly in luminosity* " 

 I have also observed that " if the air be dusty from any cause," 

 yellow light appears abundantly in the flame of the Bunsen 

 lampf; and "I have found that the column of heated air 

 arising from the flame of a spirit lamp with a salted wick is most 

 energetic in communicating yellow light " to the flame of the 

 Bunsen lamp %. I have likewise ascertained by repeated experi- 

 ments, that platinum, by mere exposure to the air, speedily 

 acquires the property of tinging flame with yellow light. 



The use of a collimator, represented at the letter B in the 

 woodcut accompanying Professors Kirchhoff and Bunsen's paper, 

 is attended with much convenience and advantage in spectrum 

 experiments where angles are to be accurately measured. This 

 method of observation was devised by me some years ago ; and a 

 detailed account of it will be found in the Transactions of the 

 Royal Society of Edinburgh, vol. xvi. and vol. xxi. p. 421. 

 I am, Gentlemen, 



Your obedient Servant, 

 Ardchapel, August 3, 1860. William Swan. 



XXII. Considerations in reference to M. Rose's Memoir on the 

 different conditions of Silicic Acid. By M. C, Sainte-Claire 

 Deville §. 



IN his valuable memoir " On the different conditions of Silicic 

 Acid ||," Prof. Rose discusses a subject which interests 

 both the chemist and the geologist, and upon which I wish 

 to offer certain considerations. Before, however, going into the 

 question, I wish to prevent the confusion which might arise from 

 a passage in M. Rose's memoir, in which, citing my researches, 

 he appears to attribute to me merit to which I am not entitled. 



He says, " Gaudin and St.-Claire Deville have succeeded in 

 melting in large drops, and drawing into wire, considerable 

 quantities of crystallized quartz, in other words, silicic acid 

 having a density of 2*6. Subsequently Deville succeeded in 

 melting as much as 30 grms. of silicic acid." 



1. I wish to observe that I have no claim whatever to the pro- 

 cesses by which M. Gaudin has been able to obtain a very ele- 

 vated temperature in a few minutes, in order to melt and draw 



* Trans. Roy. Soc. Edinb. vol. xxi. part 3. pp. 413, 414. 



t Ibid. p. 413. t Ibid. p. 424. 



§ Translated from the Annates de Chimie, vol. lix. p. 14, by Dr. Atkinson. 



|| Phil. Mag. vol. xix. p. 32. 



