340 CALCULI. 



Experiments vegetable acids. This may, probably, depend upon some 



ami observa- ^. , ^, . ., ,, . , • 



iions on urine, auction of this acid upon the uree, or colouring matter : but, 



*^^ as to the smallness of the crystals, that evidently depends 



upon the more speedy precipitation, throwing them down 

 before they can assume their natural size, and leaving but a 

 shade of difference between the crystalline and pulverulent 

 deposits. 



Exp. 14. From the above, then, we are satisfied, that 

 the vegetable and mineral acids cause a premature separation 

 and crystallization of the lithic contents of recent healthy 

 urine : but it may be observed, that this only takes place, 

 under circumstancjes not at all applicable to the living sys- 

 tem; viz. a much inferior temperature; and, in some in- 

 stances, a contact with the atmospheric air : two powerful 

 promoting causes of crystallization in general, but more 

 especially of the less soluble salts. To determine, therefore, 

 ■tihis most essential point: 



To six ounces of cold but recent urine, (in a well closed 

 phial,) were added five drops of very dilute nitrous acid, 

 vrhich were placed on a sand bath; temperature varying 

 from 80 to about 100 degrees at most. The same quantity, 

 with similar precautions, but without addition, was laid 

 aride, in the laboratory, as a standard: temperature 56 de- 

 grees. After a very short interval indeed, and almost as soon 

 as the urine acquired the temperature of between 80 and 

 80 degree's, small shining granular particles were observable 

 with a magnifier, began gi-adually to settle upon a broken 

 • kind of nubecula, or rather nubeculoe^ and to acquire colour 

 and size, though carried up and down the liquor, which 

 was in constant agitation. This experiment again twice 

 latterly repeated, and, ahvays with the same result, (care 

 being taken to keep the temperature, as nearly as possible, 

 for a few hours, between 90 and 100 degrees,) afforded 

 one of the most pleasing objects imaginable ; viz. the for- 

 ipation of this crystalline matter, under all the disadran^ 

 tages of elevated temperature, and constant agitation, from 

 (I may almost say) their primordial moleculie, to the ac- 

 complishment of their full size. And here, indeed, they 

 are most beautiful, and not to bs distinguished from these 

 jtpqn:tau€0usly d^iposited. 



The 



