56 PHYSIOLOGICAL, CHEMISTRY. 



test, so that no precipitate takes place when glucose is present, although 

 the liquid turns yellow on boiling! A very large proportion of glucose 

 may be added to fresh urine without giving rise to a pulverulent pre- 

 cipitate on the application of the test; notwithstanding that, if dis- 

 solved in pure water, it will react when present in the proportion of 

 one part to 10,000. The interference of urine with Trommer's test 

 depends, not upon its preventing deoxidation, but upon its retaining 

 the reduced copper oxide in solution, since the color of the mixture 

 changes from blue to yellow, although no precipitate takes place. It 

 is. also shown by Dr. Fowler* that if the precipitate resulting from 

 Trommer's test with a watery solution of glucose be added to boiling 

 urine, it is redissolved. The same observer has devised a method of 

 applying the test to urine containing glucose. A certain quantity 

 of urine can dissolve only a certain amount of copper oxide ; and if 

 the copper sulphate solution be added to a specimen of saccharine urine 

 in large proportion, the excess will be precipitated and show itself as 

 a deposit. A copper sulphate solution, made in the proportion of 1 part 

 copper sulphate to 7.5 parts of water, and added to saccharine urine to 

 the amount of one-half or one-third its bulk, will generally produce a 

 satisfactory reaction. 



All such sources of error may be avoided by treating the suspected 

 fluid with animal charcoal, or by evaporating it to dryness, extracting 

 the dry residue with alcohol, and then dissolving the dried alcoholic 

 extract in water, before applying the test. Either of these processes 

 will remove the substances liable to interfere with the test, 



A more delicate reagent for glucose is that known as " Fehling's 

 liquor," which is an alkaline solution of a double copper and potas- 

 sium tartrate. It is made as follows : 



Pure crystallized copper sulphate 40 grammes. 



Neutral potassium tartrate . . . . . .100 



A solution of sodium hydrate of the specific gravity 1.12 650 " 



The neutral potassium tartrate, dissolved in a little water, is first 

 mixed with the solution of sodium hydrate. Then the copper sulphate, 

 dissolved in 160 cubic centimetres of water, is gradually added to the 

 alkaline liquor, which assumes a clear, deep blue color. The whole is 

 finally diluted with water to the volume of 1154.4 cubic centimetres. 

 If one drop of this liquid be added to one cubic centimetre of a saccha- 

 rine solution and heat applied, it will detect one-fifteenth of a milli- 

 gramme of glucose by the reduction of the copper oxide. One advantage 

 of this test is that the quantity of copper salt contained in a given 

 volume is accurately known, and consequently the amount of glucose 

 in any solution may be determined by the quantity of test liquid which 

 it decomposes at a boiling temperature. One cubic centimetre of 

 Fehling's liquor is exactly decolorized by 3-73 th of a gramme of glucose. 



An inconvenience connected with Fehling's liquor is that, by expo- 



* New York Medical Journal, June, 1874, p. 632. 



