Chemical Science, 227 



7. Precipitation of Nitrate of Silver by Chlorine. — In the 

 Annales de Chiniie, torn, xviii. p. 270., it is said, in a note, that 

 a gas spoken of in the text as chlorine, could not be chlorine 

 alone, but must have contained muriatic acid, inasmuch as 

 pure chlorine cannot precipitate solution of nitrate of silver. 

 This extraordinary statement would not require notice, but that 

 it professes to be made by the editor of that work, whose 

 authority, in such a case, is so great, that it would almost lead 

 one to suppose the discovery of some new property in that 

 substance. The fact, however, that pure chlorine can preci- 

 pitate nitrate of silver, and even act on the dry salt, is so well 

 and easily established, that one must suppose the note to have 

 originated either with a careless transcriber or translator, not- 

 withstanding the R. attached to it. 



8. Analysis of Alum, and number of Alumina. — Dr. Thomson 

 has o-iven an account of his analysis of alum, made with the 

 view'^of ascertaining accurately the number of alumina. The 

 composition of alum is given as follows : 



4 atoms sulphuric acid . . 20. or 32.8542 



3 alumina .... 6.75 — 11.0882 



1 . potash .... 6. — 9.8562 



25- water 28.125 — 46.2012 



60.875 99.9998 



Or otherwise, 

 3 atoms sulphate of alumina 21.75 or 35.72885 



1 sulphate of potassa 11.00 — 18.06975 



25 water 28.125 — 46.20123 



60.875 99.99983 

 Dr. Thomson denies that alum contains any bisulphate of 

 potash. It has been said that when solutions of sulphate of 

 alumina and sulphate of potash are mixed together, a preci- 

 pitate falls consisting of alumina, the acid havmg been taken 

 from it to convert a portion of sulphate of potash mto bisul- 

 phate. On repeating the experiment with pure solutions, Dr. 

 Thomson could obtain no immediate precipitate ; but after 

 24 hours, crystals of alum were deposited. There is, there- 

 fore, no evidence of a bisulphate of potash in alum, and the 

 analytical experiments are quite against any such supposition.— 

 Annuls uf Philosophy, iii. 168. 



9. Gas from Coal Tar.— It has been found, by experiment, 

 that the coal-tar liquor, which is sometimes considered as 

 waste by those who make gas, if mixed wilh dry saw-dust, 

 exhausted logwood, or fustic, to the consistence of paste, and 

 allowed to remain till the water has drained off two cwt. of the 



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