288 Dr. Schunck on the Occurrence of Indigo-blue in Urine. 
and when V approaches the value of Vo, we have 
1:9 
P=P pp ieee 
a { '~ 374 
Let PV represent 17145, the value given (p. 336) for the actual 
product of volume and pressure at 0° C., or when T=0, then 
BV PIAS cosa ye oT i i a 1 ) 
Pav, TaTiies o'S90 C —ry0(7 =1— o74\'—590/" 
Thus we have the arithmetical absurdity of 
1 LO 1 19 
bt g90s7) a7) 590) =3= O74 
(6) Since M. Regnault’s experiments on carbonic acid have afforded 
Mr. Rankine the means of determining the value of the constant a,and 
thus enabled Prof. Thomson to predict by his calculus the thermal 
effect in passing that gas through the plug (see Table, p. 386), we 
may ask, why has the same process not afforded the means of com- 
puting the results of the experiments on air? Some explanation of 
this may fairly be expected from Prof. Thomson. 
(7) Table XII. p. 335, contains a series of experiments on air and 
carbonic acid at the temperature of about 90° C. The first part of 
this table compared with the last, shows such discrepancy, that it is 
impossible to accept the results, either in the case of air or carbonic 
acid, as established thereby. In the first part, the thermal effect in 
air would appear to be augmented by the high temperature; in the 
last, to be diminished. Prof. Thomson merely remarks that the 
lesser number is probably the more correct value, and thus that the 
thermal effect is lessened. ‘The calculus that in Prof. Thomson’s 
hands has so exactly anticipated results in the case of carbonic acid, 
appears to be of no avail in the case of air, although the experimental 
data to work upon are more abundant. 
J. J. WaTeErsTon. 
22 London Street, Edinburgh, 
August 25, 1857. 
XXXIV. On the Occurrence of Indigo-blue in Urine. 
By Evwarp Scuuncr, Ph.D., F.R.S.* 
lige occurrence of urine exhibiting various peculiar and ab- 
normal colours is a phenomenon which has frequently 
attracted the attention and excited the curiosity of pathologists. 
Of these variously tinted urmes the most remarkable and 
striking are the black and the blue, but they are at the same 
time so rare, that it has been deemed of importance to record 
minutely the symptoms exhibited in each case as well as the 
chemical and physical properties shown by the urine itself. 
* Communicated by the author from the Memoirs of the Literary 
and Philosophical Society of Manchester, vol. xiv. p. 239; having been 
read April 7, 1857. 
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