572 



exceed a few ounces, and the alkalimeter must be washed out with 

 distilled water after each operation has been finished. Care must be 

 taken to force out the bubble of air which is retained in the neck of the 

 exit-pipe before the operation begins. If it be possible, the analyses 

 should always be made in the same amount and kind of light, since 

 otherwise there will be an incorrect perception of the proper tint. 

 The direct rays of the sun, and even too bright an indirect light, must 

 be avoided as much as a deficiency of light. It is not possible to use 

 artificial light. The thickness of the layer of the solution of carbonate 

 of soda should be uniform, since there will be a difference in the tint 

 and the rapidity of its production in the shallower and the deeper parts. 

 From one to two minutes must be allowed for the production of the 

 colour when it approaches the standard tint. Dr. Guy's spatula is to 

 be preferred to Dr. Beale's suction-tube, since it retains a less quantity 

 of the thick fluid from the previous immersion. It often occurs, in 

 the analysis of coloured urine (as in urine of high specific gravity), 

 that the distinction of the tint is not well appreciated if the solution 

 be added in quantities of one division only ; and hence it is often 

 better for the experienced investigator to add two divisions of the 

 solution at a time, so as to produce a little excess of colour, and then 

 to compute and deduct the excess. In urine of low specific gravity, 

 the tint is quickly and distinctly produced by half a division of the 

 solution. The specific gravity of healthy urine is a ready guide to 

 the addition of the first and large quantity of the solution. In a 

 healthy person, and one of regular habits and under ordinary condi- 

 tions, the daily quantity of chloride of sodium which is eliminated 

 and must be deducted from the urea is tolerably uniform ; and the 

 quantity having been ascertained by numerous trials, it may be used 

 for the same person as a constant quantity, where absolute accuracy 

 is not essential, and thus the labour will be materially lessened. 

 With urine of a specific gravity from 1012 to 1025, it is convenient 

 to add by the pipette an ounce of urine to i ounce of the baryta 

 solution. When the specific gravity exceeds 1025 (in the absence 

 of sugar), equal parts should be used ; when it is below 1012, it is 

 needful to add 3 or 4 parts of urine to 1 part of baryta solution, and 

 with diabetic urine 4 parts should always be added. A quarter of an 

 ounce of the mixed fluids should be taken with the pipette, and the 

 number of divisions of the mercurial solution used to produce the 



