235 Scientific Notices^^Mirieralog^. [SEPt. 



ing ; but the potash thus prepared gave ammonia, when heated 

 with zinc, in hydrogen gas." 



" Potash is not the only substance which produces this effect 

 with the metals and vegetable substances. Soda produces it; 

 so also, does lime, and baryta, the latter not being so effective 

 as the former, or producing the phenomena so generally. The 

 common metallic oxides, as those of manganese, copper, tin, 

 lead, &c. do not act in this manner. 



" Water or its elements appear to be necessary to the experi- 

 ment. Potash or soda in the state of hydrates generally con- 

 tain the water necessary. Potash dried as much as could be 

 by heat, produced little or no ammonia with zinc ; but re-dis- 

 solved in pure water and evaporated, more water being left in it 

 than before, it was found to produce it as usual. Pure caustic 

 lime, with very dry linen, produced scarcely a tmce of ammonia, 

 whilst the same portion of linen with hydrate of lime yielded 

 it readily, 



" The metals when with the potash appear to act by, or ac- 

 cording to, their power of absorbing oxygen. Potassium, iron, 

 zinc, tin, lead, and arsenic evolve much ammonia, whilst 

 spongy platina, silver, gold, Sec, produce no eflect of the kind. 

 A small portion of line clean iron wire dropped into potash 

 melted at the bottom of a tube, caused the evolution of some 

 &mmonia, but it soon ceased, and the wire blackened upon its 

 surface ; the introduction of a second portion of clean wire 

 caused a second evolution of ammonia. Clean copper wire, in 

 fused potash, caused a very slight evolution of ammonia, and 

 became tarnished." 



Mineralogy. 



2. SuIpIuito-lri-carbo)iale oJ'Lead, 



M. Str.omeyer has lately examined the sulphato-tri-carbonate 

 of lead, whose composition was first pointed out by Mr. Brooke. 

 His results, which confu-m the conclusions of the latter gentle- 

 man, give, for the constituent elements of the mineral, 



Carbonate of lead 72*7 



Sulphate of lead 27*3 



and it consequently consists of one atom of sulphate of lead and 

 three atoms of carbonate of lead, as previously determined by 

 Mr. Brooke. 



3 . Hydrate of Magnesia . 

 A specimen of native hydrate of magnesia from Swinaness, in 

 Unst, examined by M. Stromeyer, gave 



