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XXIX. A Letter on the Differences in the Structure of 

 Calculi, which arise from i heir being formed indifferent 

 Paris of the urinary Passages; and on the Effects that 

 are produced upon them, ly the internal Use of solvent 

 Medicines*, from Mr. William Brande to Everard 

 Home, Esq,, F.R.S* 



" DEAR SIR, 



.Having availed myself of the opportunity you procured 

 for me, of making a chemical examination of the calculi 

 contained in the Hunterian Museum, as well as those in 

 your own collection, I herewith seud you an account of 

 what I have done. 



Should the observations appear to you to throw any new 

 light upon the formation of calculi/ I request that you will 

 do me the honour of laying them before the Royal Society. 



The collection which I have examined, is not only un- 

 commonly large, but the greater part of the specimens have 

 histories of the case annexed to them. 



This circumstance enabled me not only to ascertain the 

 situations in which the calculi were found, but likewise many 

 of the circumstances attendant on their formation. 



I have therefore endeavoured to form an arrangement 

 upon these principles, with a view to render the subject 

 more clear and perspicuous, 



Section L 



Of Calculi formed in the Kidneys, and voided without having 



afterwards undergone any Change in the urinary Passages, 



These have the following properties : 



They are of a brownish yellow colour, sometimes of a 

 grayish hue, which seems to arise from a small portion of 

 dry mucus adhering to their surface. 



They are entirely soluble in a solution of pure potash, and 

 during their solution they seldom emit an odour of ammonia. 



When heated to dryness, with nitric acid, the residuum 

 is of a fine and permanent red colour. 



When exposed to the action of the blow-pipe, they 



f From Philosophical Transactions for 1 308. 



h 4 blacken 



