tf4 Inquiry into the Laius of AJinitfl 



heat, ic expels thofe acids from their combinations ; if attention had at the fame time been 

 paid to the fafl:, that'even by the heat employed for caufing the evaporation and obtaining 

 the cryftallifation of falts, the proportions of the volatile acids may be confiderably changed 

 by the fulphuric acid which remains oppofed to them, and which may even at laft expel 

 them entirely, by means of the difference which exifts between its fixity and that of thofe 

 acids. (Art. VII. No. 5). 



10. We are indebted to Bergman for fome ufeful obfervations relative to the errors that 

 may originate from the folubility of a fubftance which is difengaged, and of which the 

 feparation is not perceived. He remarks that pot-afli or foda do not afFe£l: the tranfparence 

 of a folution of fait with bafes of lime, if this folution be diluted with fifty times its quan- 

 tity of water ; becaufe the lime which is feparated, being foluble, remains in the water. 

 But he does not confider that if the lime did then poffefs only its natural folubility, this 

 would be a very feeble obftacle to the precipitation ; for it would require nearly feven 

 hundred parts of water to effeft its folution. What adds fo greatly to its natural folubility 

 is, that it continues to remain in combination with the ac4d (Art. V. No. 5), and that it 

 cannot be feparated without retaining a part of this acid (Art. III. No. 9), by which its 

 iolubllity is fo increafed. 



11. Notwithftanding his general obfervations, Bergman has miftaken the efFefts of 

 folubility in a variety of circumftances. For inftance, he did not believe that the nitric 

 and muriatic acids were capable of ading upon the phofphate of lime, though the only 

 difference that can be afcertained in this refpeft between thefe acids and the fulphuric, 

 ■without being acquainted with the comparative force of their affinities, is, that the two 

 firft-mentioned only form foluble combinations, while that produced by the fulphuric acid 

 may in a great meafure be withdrawn by the force of cryftallifation. 



12. It is the folubility of lime, as well as of barites, acquired by the a£l:ion of the acid, 

 upon thofe earths, which prevents ammonia from affording any precipitate in the folution 

 of thofe falts of which they are the bafe. Ncverthelefs the firft portion of ammonia which 

 IS mixed, for inftance, with the muriate of lime, emits fcarcely any fmell, which indicates 

 that it has entered into combination ; and its adion may be rendered perceptible, as we 

 fliall fhew. 



I mixed fome ammonia with a folution of muriate of lime, and evaporated the liquid 

 in a retort. When it was reduced to a certain point, a confulerable quantity of pre- 

 cipitate was formed. I continued the experiment : towards the end the quantity of pre- 

 cipitate was much diminiftied : a pellicle was formed, and by cooling a great quantity of 

 cryftals in needles of a tolerable length were obtained. It was a triple fait, from which 

 ammonia might be difengaged by lime. This fait, on being again diffolved and evaporated 

 in the open air, no longer afforded indications of ammonia when tried by lime. 



It is therefore evident, that when the water was not too abundant, the ammonia pre- 

 cipitated part of the lime, though it was rendered much more foluble by the acid, and 

 though the a£lion of the ammonia was confiderably weakened by heat, which dimlnifhed 



both 



