ITS ANALYSIS. 433 



We have already noticed the mode of detecting butyric add, 

 certain abnormal pigments, and ammonia. 



With a view of determining the average quantitative relations 

 of certain inorganic constituents, the same reagents are generally 

 employed which are used in their qualitative analysis; thus, for 

 instance, in order to detect an excess or a deficiency of hydro- 

 chloric, phosphoric, and sulphuric acids, and lime, in the urine, 

 nitrate of silver, acetate of lead, chloride of barium, and oxalate of 

 ammonia are usually directly added to separate specimens of urine 

 a mode of proceeding which can scarcely be justified, even in a 

 medico-diagnostic investigation. Care should at all events be 

 taken to bring the different samples of urine which are to be com- 

 pared with the normal secretion to the same degree of density by 

 concentration, since it is by this method only that a comparison 

 can be made between the volumes of the precipitates. Such a 

 method would, however, consume more time than observers are 

 willing to expend on the inquiry, although it must be obvious that 

 such a comparison of the volumes of the precipitates cannot in 

 itself lay claim to the slightest degree of accuracy. How many 

 substances may not be contained in the precipitated metallic salts, 

 even where nitric acid has been most carefully employed for the 

 recognition of the chloride of silver or the sulphate of baryta ? 

 May not numerous organic substances be precipitated by the 

 metals from the urine, more especially when it is in a morbid con- 

 dition ? How is it possible to decide regarding the density of the 

 urine from its colour, or in this manner to determine the excess, or 

 diminution, of these substances ? Physicians should be cautious, 

 lest they may be led into new errors by these superficial chemical 

 tests, when they have only just liberated themselves, by physical 

 and anatomical investigations, from older misconceptions. It would, 

 however, be going too far, were we to attempt wholly to avoid these 

 misapplied methods, in entering upon a scientific examination of the 

 urine. Thus, for instance, in attempting to ascertain the increase, 

 or diminution, of the phosphates in any disease, we might, after 

 collecting the twenty-four hours' urine, and keeping it as cool as 

 possible, add ammonia in order to remove the earths and the 

 greater part of the uric acid, and then treat the filtered fluid with 

 sulphate of magnesia. The first precipitate after exposure to a red 

 heat would show the amount of the earthy phosphates, and from 

 the second we could calculate the phosphate of soda. If we wish to 

 ascertain the quantity of lime separated with the urine in a certain 

 time, it would be sufficient to precipitate the filtered urine with 



VOL. II. 2 F 



