54U /]nit!\Jis of Tin Ore,— Fairy Rings. 



In the mean lime, as wc are forced to admit that all the oxygcne of the ore is found in 

 the alkaline folution, the more efte£tual a£lion of the acid upon the metal cannot be fup- 

 pofed to arifc from the lofs of a portion of this principle, becaufe it continues flill in the 

 fame ftato of f.ituration ; neither is there any fign of oxygenated muriatic acid gas ; and it 

 would likewifc be difficult to conceive, why in this circumftance tliere (hould rather be a 

 dlfcngagement of the gas than when the acid is digeftcd on the ore, as is obferved in the 

 oxides of mangancfc and of lead. 



To eilablifli this point of theory on a more decifive experiment, I diflblved .fix grammes 

 of tin in the nitric acid, and evaporated feveral times to drynefs the new acid which was 

 fuccedivcly poured on. I fuppofe it cannot be doubted but that the tin in this ftate had 

 combined with as much oxygene as it is capable of fixing. Neverthclefs, the mafs of 

 white oxide, wafhed until the water which came off caufed no further change in vegetable 

 colours, was very foluble in muriatic acid. 



What therefore is the caufe of tlie infolubility of the ore, which confifts alfo of tin and 

 oxygene with fcarce one hundredth part of foreign matter ^ This caufe is to be found on- 

 ly in the Hate of aggregation of the latter. This aflcrtion cannot be thought (Irange, ex- 

 cept on account of the little regard which has hitherto been paid to its energy. If com- 

 binations be the refult of affinity or ele£Vive attraflion, is not this attraftion itfelf a power 

 which may be rendered ineffeflual by the fum of the forces which a£l in the contrary di- 

 rection .' Thefe truths furely cannot appear repulfive to Mr. Klaproth, who has ren- 

 dered them fo evident, by fliewlng that the ruby, the fapphire and the adamantine fpar, 

 of which the elements are in their own nature fo eafily foluble, do not refift the ordinary 

 methods of analyfis but in confequence of the aggregation of their integral parts. 



VI. 

 On Fairy Rings. 



A HE appearance in the grnfs, commonly called Fairy Rings,' is well known. It con- 

 fiils cither of a ring of grafs of more luxuriant vegetation than the reft, or a kind of cir- 

 cular path in which tlie vegetation is more defeflive than elfewhere. It appears to be 

 pretty well afcertained, that the latter ftate precedes the former. Two caufes are affigncd 

 for this phenomenon : the one, which cannot be controverted, is the running of a fungus ; 

 the other, which has been confidered as an effufion of theory, is grounded on a fuppofition 

 that the cxplofion of lightning may produce effeds of the fame kind on the ground as 

 Di:. Prieftley's battery was found to produce on the poliflied fuiface of a plate of metal, 

 that is to fay, a feries of concentric rings. Some obfervations, Mhich I find in my com- 

 mon-place book, appear to fliew that this laft effeft may, in certain cireumftances, take 

 place. 



On Tuefday the 19th of June, 1781, a very powerful thunder-ftorm pafled over the 

 weftern extremity of London. I was then at Batterfea, and made n6 other remark on the 

 phenomena than that the explofions, which were very marked and diftinft, were in many 

 •iiift.inccs forked a 'the lo^^■er end, but never at the top ; whence it follows, that the clouds 

 w'te in the poCtiv « ftate for the moft part. On the following Sunday, namely the 24th, 



I happened 



