On the mutual Affinities of the Earths. 487 



fcience. It may be denominated a falfe key, but nevcrthelefs, fuch as may aflift us, in 

 our approach certain objefts which we fhould not otherwife behold, but confufedly and 

 at a diltance. 



A third truth, which has certainly ftruck all thofc who have meditated upon the true 

 objeft of a methodical claffification, is, that the properties which exclude, are yery diffe- 

 rently charadleriftic from thofe which bring objcfts together. This arifes from the cir- 

 cumftance, that in the confufed accumulation of circumftances of refemblance, frequently 

 ill determined, we find no bafis of fufEcient folidity to afcertairt our divifionS) except in 

 the oppofitions prefcnted by fuch cxpreflions as fubftances decompofed or not decompofed, 

 combuftible and incombuftible, dudtile and not duftile, foluble and infoluble, and the 

 like. Thefe principles being eftablifhed, we have here to confider the fafts of both kinds > 

 thofe which exhibit an analogy between other fubftances and alkalies, and fuch other fa£ls 

 as form oppofitions between them. 



Among the former it is remarked, that magnefia may unite with fulphur; that magnefia 

 and alumine produce the faponaceous ftatc in oils ; that the metallic oxides alfo form foap -, 

 that the oxides of lead and iron * produce the fame effedl as the alkalis in the vitrification 

 of earths, particularly filex, &c. &c. 



With regard to the fa£ls which eftablifh an oppofition, and which we have obferved to 

 be the raoft conclufive, it is fufEcient to obferve, that the alkaline carbonates' are foluble 

 In water, but thofe of the three earths arc not ; that the fame difference cxifts between the 

 alkaline and the earthy foaps, in which refpeft the latter have a much greater refemblance 

 to the metallic foaps ; that the fixity of the earths is much greater than that of the alka- 

 lies ; and to conclude, by a ftill more ftriking fa£t, the alkalies are (bluble in alcohol, and 

 the earths infoluble. If a fufficlent quantity of alcohol be poured into an aqueous folution 

 of barytes, the liquor is foon rendered turbid by fmall white flocks, which in a few minutes 

 fall to the bottom of the veflel, and leave the fluid no longer capable of altering the co- 

 lours of culcuma and fernambouc. 



From the experiments and obfervatlons contained in this memoir, I think the following 

 conclufions may be drawn : 



There is a tendency to union exifting between all the earths, as well in the humid as in 

 the dry way, which according to the degree of ele£live attraftion, determines their preci- 

 pitation from a common folvent and their vitreous compofition. 



The union of two earths operates llke'the alloy of two metals, by virtue of the fame 

 law, which excludes the fuppofition of a property in one of the two bodies which may 

 belong to another order. 



By comparing the refults of thefe attradions to the folutions, by any faline fubftances 

 whatfoevcr, alkaline or acid, we fhould be often embarraffed to point out which of the 



* Mr. KIiwKn has ftiewa, that the oxide of iron, in a double or triple proportion, caufej filex, and even 

 magnefia to flow ; that alumine mixed with two parti of oxide of iron is fufible at iCa degrees of the 

 pyrometriefcale of Wedgwood. Mineralogy I. 71. 



3 R 2 . ' earths 



