1877.] 



Sugar in relation to the Blood. 



319 



This suffices for all the sugar to be oxidized, aud accordingly for all the 

 required action upon the copper solution to occur. There is no risk 

 during this time of spontaneous change occurring in the copper solution; 

 but observation has shown that should boiling be continued for a 

 lengthened period (by which I mean ten minutes or a quarter of an 

 hour) the copper solution undergoes alteration, and no longer possesses 

 the power of resisting spontaneous reduction. As regards the amount 

 of copper solution, 10 c. c. of the test of ordinary strength are found to 

 be more than sufficient for 20 c. c. of the blood of animals in a natural 

 state. Where from any cause an extra quantity of sugar exists, more in 

 proportion of the test-solution is of course required. 



The precipitated suboxide of copper has now to be separated from the 

 excess of copper solution. Experience shows that filtration through 

 filter-paper cannot be resorted to for the purpose. In the first place, the 

 pores of the paper tend to become blocked up and filtration to be stopped ; 

 and in the next (and this is a fatal objection) the paper absorbs and so 

 tenaciously holds some of the copper solution that it cannot be effec- 

 tually washed out. A plug of asbestos, in a filter-funnel, may be used 

 instead ; but it is not always easy to procure the asbestos with fibres of 

 the medium state of fineness to answer well for speedy and, at the same 

 time, delicate filtration. A material, however, which has recently been 

 introduced, viz. glass-wool, exactly furnishes what is wanted. Properly 

 packed in the neck of a funnel, it permits filtration to be effectively and 

 speedily performed ; the state of the filtrate readily shows if the plug 

 has not been sufficiently closely packed to keep the whole of the precipi- 

 tate back. 



Should the crystallization of the sulphate of soda in this or the pre- 

 ceding filtration interfere with the process of filtration, the funnel may 

 be lodged upon a beaker containing fluid kept in a state of ebullition. 

 Through the heat thus applied, the liquid is prevented from assuming 

 a crystalline form. 



The suboxide having been collected and washing with distilled water 

 performed, it is returned to the beaker in which the reduction was effected, 

 to secure that whatever precipitate may have been adhering to the sides 

 of the vessel is retained. The plug is simply pushed with a glass rod 

 from the funnel inverted over the beaker, and the funnel w T ashed and its 

 surface cleaned from all adhering precipitate. We have now the sub- 

 oxide in a fit state to dissolve ; and until I resorted to the use of peroxide 

 of hydrogen to effect its oxidation a difficulty presented itself in this 

 part of the operation, the precipitate requiring an amount of acid to 

 dissolve it which interfered with the subsequent deposition of copper by 

 galvanic action. After the addition of a few drops of peroxide of hydro- 

 gen, a very small quantity of nitric acid (a few drops only) is sufficient 

 to lead to instantaneous solution ; and after boiling to decompose the ex- 

 cess of peroxide of hydrogen, the contents of the beaker, consisting of 



VOL. XXVI. Z 



