APPARATUS. 333 



cific gravity becomes 1.12, or the specific gravity imiy 

 be determined by the use of Baume's hydrometer, which 

 should float at 16J. To each 1,000 grains of this solu- 

 tion add 259.90 grains of purecn/sto^ecZRochelle salts. 

 This constitutes the caustic solution. 



One volume of the copper solution mixed with two 

 volumes of the caustic solution forms Fehling's Stand- 

 ard Solution, 200 grains of which are equivalent to one 

 grain ot sugar. 



These solutions must be kept separate until wanted 

 for use, mixing only the quantity required from time to* 

 time. The copper solution is quite stable, but the other 

 is liable to deteriorate by keeping. It will be advisable 

 for the practitioner to use the caustic solution from an 

 ounce bottle fitted with a tight stopper, which can be 

 refilled from time to time, the stock bottle being kept 

 in a cool, dark place. On mixing the two together a 

 precipitate forms which will immediately disappear on 

 shaking. Should, on boiling the same, the liquid retain 

 a clear blue color, it is in good condition. Heat should 

 always thus be applied in advance. By complying with 

 the directions given, the caustic solution can be kept in 

 order for years ; and it is well to make enough at once 

 to last for at least a year, and the physician is reminded 

 that this Fehling's test for sugar is daily in demand. 



Test of Standard Solution for Sugar. Dissolve four 

 grains of pure grape sugar in 400 grains of water. 

 This solution should always be used when freshly made. 

 In the preceding analysis it will be observed that the 

 burette has been filled with the standard solution. Now 



