1873.] 



On Rainfall and Sun-spot Periodicity. 



297 



this amount of heat ; and when the glowing charcoal, in the case of Jey- 

 poorite, is afterwards held under the nose, a distinct and even strong 

 smell of garlic is perceived. If fusion of the gold takes place, this smell 

 ceases immediately. There is also emitted from Jeypoorite thus treated 

 another very peculiar but indescribable smell, after that of garlic has 

 ceased. This I believe to be due to volatilizing antimony ; and the fact 

 is, so far as I know, unnoticed by writers on the "blowpipe" since the 

 time of Cronstedt ; but Yon Engestrom says of this metal (Translation of 

 Cronstedt's 'Mineralogy,' by Grustav von Engestrom, London, 1772, 

 p. 308), " Antimony is known by its particular smell, easier to be dis- 

 tinguished, when once known, than described." The corrosion of plati- 

 num by Jeypoorite powder, mixed with a large amount of rust, when 

 roasted through it, is also (in my opinion) a strong proof of the existence 

 of sulphide of antimony (vide " Pyrology," par. 80) ; for in this case I 

 found that, thus roasted, Jeypoorite considerably, and even pure Sb 2 3 

 slightly corroded the platinum, while native arsenic and arsenic acid did 

 not do so at all. 



(21) When the gold ball, placed with a crystal of Jeypoorite on char- 

 coal, as described in (20), is fused by an O. P., the surrounding ash of 

 the charcoal is observed to be tinged with a beautiful rose tint. This 

 phenomenon appears to be due to the formation of arseniate of cobalt, and 

 to be analogous to that of Erythrine in nature, where the cobalt oxide, 

 combining with arsenic acid, is hydrated with the water absorbed chemi- 

 cally from the atmosphere by the latter. Cronstedt (' Essay towards a 

 System of Mineralogy,' Lond. 1772, Sect, ccxlvi. p. 230) notices this fact 

 under the article " Cobalt," which, he says, " w 7 hen united with the calx 

 of arsenic in a slow (not a brisk) calcining heat, assumes a red colour : 

 the same colour is naturally produced by w T ay of efflorescence, and is then 

 called the bloom or flowers of cobalt." The fact proves the truth of 

 Gmelin's assertion, that fusing gold takes up a certain portion of arsenic* 

 Another proof seems shown in the fact that the gold ball thus treated, 

 assumes on the surface, when rapidly and momentarily heated, a dark 

 reddish, and even a copper-coloured yellow, which may be the so-called 

 "rose-colour" said to be given to gold by Indian goldsmiths, but which I 

 have never yet seen in any part of India. 



III. " On a Periodicity of Rainfall in connexion with the 

 Sun-spot Periodicity.^ By C. Meldrum, Director of the 

 Meteorological Observatory, Mauritius. Communicated by 

 Sir Edward Sabine, K.C.B., F.R.S. Received April 6, 1873. 



Assuming that there is a sun-spot periodicity, in the course of which 

 the sun undergoes a variation with respect to heat or some other form of 

 energy, we should expect to find a corresponding variation in the state of 

 our atmosphere. 



