Chemical Science. 173 



tances. The intensity of the flash will be produced by the quan- 

 tity of electricity contained in the immense stratum enveloping 

 the cloud. If the stratum is not continuous, which is very pos- 

 sible in so bad a conductor as a cloud, or if all the electricity 

 spread over the space occupied by the cloud has not had time to 

 disengage itself, so as to arrive at the surface of the cloud, the 

 discharge will only be partial, and then the redoubled peals of 

 thunder will easily be understood. It appears impossible to us, 

 according to these observations, that the thickness of the electric 

 stratum can ever be any thing like so great on the surface of a 

 thunder cloud as on that of a solid conductor ; for the repulsion 

 of its molecules would dissipate it in the air. We perceive no- 

 thing to retain it but the resistance of the air as a non-conductor, 

 and that resistance can be but very small. 



As the primitive electricity spread over the space occupied by 

 a thunder-cloud can unite but very slowly into a thin stratum, it 

 becomes difficult, according to the theory of Volta, to attribute 

 to it the formation of hail in particles as large as those which are 

 sometimes observed ; the phenomenon, however, is certainly con- 

 nected with atmospheric electricity ; and though we are not ac- 

 quainted with all the circumstances which would enable us to com- 

 prehend it, we must not reject a cause because it appears to us not 

 to have an intensity proportional to the effects we would explain. 

 — Ann. de Chim. xxix. 105. 



4. On the Existence of Iodine in a Mineral Substance. By 

 M. Vauquelin. — The mineral in which M. Vauquelin has, for 

 the first time, found this peculiar substance, was brought by 

 M. Joseph Tabary from the neighbourhood of Mexico, and was 

 labelled virgin silver in serpentine. It was of a whitish colour 

 on its rubbed surface, presenting grains of metallic silver ; its 

 fracture was lamellated, and of a yellowish green colour, witli 

 some black portions and metallic silver. Twenty parts of the 

 substance were acted upon by nitric acid with effervescence ; being 

 boiled with it for some time, and then diluted, two insoluble 

 portions appeared ; one very heavy, and falling instantly, whilst 

 the other was light, and remained in suspension. When sepa- 

 rated and washed, the first weighed 6A2 parts ; it fused easily by 

 the blow-pipe, producing a purple flame, and ultimately a small 

 globule of silver appeared in the centre of a fused mass like 

 chloride of lead. The edges of the charcoal were covered with a 

 yellow powder. The lighter matter was brown, and weighed 2.7 

 parts ; it burnt, producing sulphurous acid, and leaving sulphuret 

 of lead with a little iron=1.5S parts. 



A portion of the first matter, heated with muriatic acid; gave 

 a red brown colour, and produced slight effervescence with the 

 odour of chlorine. As the temperature rose the effervescence in- 



