ITS ANALYSIS. 431 



of soda in the urine, the addition of the sulphate of magnesia causes 

 a precipitation of phosphate of magnesia and ammonia, from which 

 we must calculate the ammonia. There are, however, two points 

 to be borne in mind, if we would wish to obtain accurate results 

 by this method ; the first is, that the bicarbonate of soda throws 

 down some ammonia with the magnesia ; and the second is, that it 

 is possible that there may not be sufficient phosphate of soda in 

 the urine to combine all the ammonia with the magnesia, and to 

 precipitate them. Both these difficulties may, however, be readily 

 overcome; the former, by determining the magnesia in the pre- 

 cipitate thrown down by the bicarbonate of soda, the latter, by 

 the addition of an excess of phosphate of soda (Berzelius*). 



The occurrence of nitric acid, which Proutt and WurzerJ 

 believed that they had discovered in brickdust sediments, is very 

 doubtful ; for the methods of analysis which they employed might 

 very easily deceive them. 



In considering the analytical methods which have been em- 

 ployed, or suggested, for the examination of the urine, we find 

 ourselves upon one of the most unpromising fields of inquiry 

 within the whole domain of physiological chemistry. Our remarks 

 as to the time and labour that have been lost in examining the 

 analyses of the blood, apply with still greater force to most ana- 

 lyses of the urine. For these very analyses have been the means 

 of throwing so much disrepute on the zoo-chemical investigations 

 of true chemists, that they have been classed in the same cata- 

 logue with the much condemned analyses of old and modern drugs. 

 We will only add a few remarks to what has been already stated 

 in the first volume, in reference to the modes of discovering, 

 and the methods of determining, individual constituents of the 

 urine. 



But if pathology has hitherto reaped only little advantage 

 from analyses of the urine, the fault rests less with chemists than 

 with physicians, who obviously can benefit little, or nothing, from 

 even the best analyses of the urine, as long as they continue 

 in error as to the actual results which may be obtained from such 

 investigations. Till they learn to comprehend the questions they 

 would submit to the chemist, they cannot obtain the desired reply 

 from pathological chemistry. As long as the physician thinks he 

 may employ chemical reagents as mere diagnostic instruments, like 



* Jahresber. Bd. 17, S. 628. 

 t Op. cit. 

 J Op. cit. 



