440 URINE. 



tube running along the bottom of the vessel. By these methods, 

 which are familiar to all chemists, the faintest breath may be ob- 

 served upon the exterior or interior of the glass. We simply refer 

 to this well-known operation, in order to show those less familiar 

 with this apparently simple method, how much care and attention 

 are required for the mere determination of the specific gravity of a 

 fluid. 



Having already offered these remarks on the methods of deter- 

 mining the specific gravity, it may not appear superfluous to 

 observe that we have been induced to adopt this course on two 

 different methodological grounds. The first, which has already 

 been noticed, refers to the necessity for the utmost accuracy where 

 we are desirous of imparting any scientific value to our determi- 

 nations of density as a controlling test of the chemical analysis, 

 and as a means of comparison with the specific heat and the 

 refractive and polarizing powers; since, without such precau- 

 tion, the scientific object of the inquiry could never be attained. 

 The method alone is not all that ought to be considered, since the 

 mode of its application is of even greater importance ; for whilst 

 one person may obtain very incorrect results in weighing with the 

 most accurate balance, another may contrive to arrive at the best 

 determinations by means of an inferior balance, provided the 

 weights are accurate. Thus, too, the second reason which has 

 led us into some diffuseness, is obvious from our previous obser- 

 vations, and consists in this : that we should regard all average 

 estimates of density which are prosecuted simply by way of ap- 

 pendage to the chemical analysis, or for the purpose of roughly 

 determining the quantity of water in a fluid, as entirely superfluous, 

 and a mere waste of time and labour which might have been 

 expended upon some of the numerous questions of science which 

 still require elucidation. 



In passing to the consideration of the quantitative analysis of 

 the urine, we need only observe generally, that in all investigations 

 of the urine, in which the quantitative relation of the secreted 

 urinary constituents is to be ascertained, the collective fluid which 

 has been passed within a definite period (as, for instance, twenty- 

 four hours) should be selected for analysis, and its composition 

 compared with that of other normal or morbid urine which has 

 been passed in the same period of time ; or in case this method is 

 not practicable, or is otherwise unsuited to the object of the inves- 

 tigation, the quantity of water should be wholly disregarded, and 

 the proportions of solid constituents to one another should be made 



