48& On the mutual Affinities of the Earths. 



water fliould be added fucceflively for four or five times before the diftlllation be urged 

 to drynefs ; after which the veflels are to be left to cool without difturbance. At the 

 bottom of the retort will be found fmall grains, exhibiting very perceptible faces and 

 anglcs> and which muft not be confounded with the pellicle ufually formed by the car- 

 bonate of lime. 



barytes, ftrontian, and lime alfo poflefs in common with the alkalis, the property of 

 giving a green colour to the fyrup of violets, a red to curcuma, and of reftoring blue co- 

 lours,, which have been reddened by acids ; and this, in the language of accurate chemiftry, 

 implies nothing more, than that thefe fubftances have a ftronger affinity to the acids, than 

 is poflefled by the colouring matter itfelf. I have elfewhere fliewn, that tin and iron like- 

 wife reftore the blue colour by feizing the acid *. 



From the experiments before related, it follows that the three earths have, as well as the 

 alkalis, Jt decided afEnity with filex and alumlne, as well in the dry as in the humid way; 

 fo that lime, takes filex from pot-afli, and feizes the alumlne at the inftant it is abandoned 

 by the folphuric acid. 



The adlion which thefe earths exercife upon the oils, the foaps, and animal matters, 

 the union they contraft with the Pruffian colouring principle, fulphur, and the acids, form 

 fo many new points of refemblance with the alkaline fubftances, 



Thefe numerous refemblances cannot be difputed, and appear at firft fight to demand 

 a common claflTical denomination, but does this opinion agree with found principles i arc 

 there not alfo fafts which oppofe It. It will be proper to examine this point. 



All bodies have common properties more or lefs numerous ; fo that in order to denote 

 their qualities rigoroufty, it will be proper to admit two clafles only, or to diftinguilh them 

 under two relations ; the firft comprehending fimilar bodies, or thofe which have all their 

 properties alike, and the latter thofe which have not this condition, or poflefs diftinil 

 properties- 



In the fecond place, the properties of bodies are almoft invariably the different degrees 

 of the fame efre£l. We call thofe fubftances fufible, which flow without requiring an 

 intenfity of heat greater than that of our common furnaces ; we fay that a fubftance is 

 foluble, when it dllTolves in water to a certain quantity; that fuch a body Is fixed, becaufe 

 it docs not rife in vapour, but with great difficulty, and in the fame manner we fpeak of 

 other properties. The limit of our clalTes is always the refult of fuch comparifons ; and 

 as we can fcarcely find two fubftances which ought to be placed abfolutely on the fame 

 line, it follows that we muft either renounce clafHfication, or give a certain extent to our 

 limits, by means of which fimilar effects, though very difproportioned, may ferve by their 

 connexion to determine the moft efTential charadlers. 



A long fuccefTion of ufelefs efforts ought to convince us, that nature has prepared no- 

 thing for our methods ; but this is not a reafon why we (hould deftroy this inftrument of 



• Recherche? fur la matiere colorante des vegetaax, &c, Ann. Ue Chemie, torn, xxx, p. i8j. 



fcience. 



