331 



amount of this is considerable, a brown extractive, sometimes in 

 large quantity, the aqueous solution of which, by exposure to air, 

 yields a further supply of coloured indigo, and which closely re- 

 sembles hcematin in its chemical manifestations and elementary com- 

 position. There is therefore great reason for believing that in the 

 majority of the cases here recorded, the blue indigo was derived 

 from altered heematin, although it is at the same time probable, that 

 in some cases it is formed from modified urine pigment which is 

 itself supposed to be a modification of heematin. Between the greater 

 number of the animal colouring matters there is the closest relation- 

 ship in chemical composition, so that the transformation of the one 

 into the other would appear to be both easy and natural. 



4thly. That the urines in which the coloured indigo occurs in the 

 largest quantity, are usually of a pale straw colour, readily beco- 

 ming turbid, alkaline, and of low specific gravity. Small quantities 

 of indigo are however frequently found in urines possessing charac- 

 ters the very reverse, that is, in such as are high-coloured, acid, and 

 of high specific gravity ; but, as a rule, in these urines the blue pig- 

 ment is usually absent. 



5thly. That as coloured indigo does not occur in healthy urine, 

 and since where the amount of this is at all considerable it is ac- 

 companied with strongly-marked symptoms of deranged health, the 

 formation of blue indigo in urine must be regarded as a strictly 

 pathological phenomenon, apparently associated rather with some 

 general morbid condition, than essentially with disease of any one 

 organ ; although there is reason for believing that the blue deposit 

 is met with very frequently in Bright's disease, and in affections of 

 the organs of respiration, it should however be remarked that none 

 of the worst cases of indigo in the urine which the author met with 

 were cases of Bright's disease. 



The paper is illustrated by drawings, and a specimen of the indigo, 

 as deposited from urine, was exhibited. 



5. "On the Thermal Effects of Elastic Fluids." By Professor 

 William Thomson, F.R.S., and J. P. Joule, Esq., F.R.S. Received 

 June 15, 1853. 



The authors had already proved by experiments conducted on a 

 small scale, that when dry atmospheric air, exposed to pressure, is 

 made to percolate a plug of non-conducting porous material, a de- 

 pression of temperature takes place increasing in some proportion 

 with the pressure of the air in the receiver. The numerous sources 

 of error which were to be apprehended in experiments of this kind 

 conducted on a small scale, induced the authors to apply for the 

 means of executing them on a larger scale ; and the present paper 

 contains the introductory part of their researches with apparatus 

 furnished by the Royal Society, comprising a force pump worked by 

 a steam-engine and capable of propelling 250 cubic inches of air per 

 second, and a series of tubes by which the elastic fluid is conveyed 

 through a bath of water, by which its temperature is regulated, a 

 flange at the terminal permitting the attachment of any nozle which 

 is desired. 



