METABOLIC PROCESSES IN THE PLANT. 295 



with potash, and made up to 500 c.c. 1 We now heat dilute Feh- 

 1 in IT'S solution on the water- bath in an evaporating dish, add 20 

 c.c. of the sugar solution, and again heat for ten to fifteen minutes.* 

 The Cuprous oxide formed is collected as rapidly as possible on a 

 filter, washed with hot water and dried. We now ignite the filter 

 paper and strongly heat the Cuprous oxide in a platinum crucible 

 with addition of a little Potassium nitrate, and finally determine 

 the weight of the Cupric oxide obtained. 220'5 parts of the 

 Cupric oxide correspond with 100 parts of grape-sugar, or 90 

 parts of starch. The requisite Fehling's fluid is prepared as fol- 

 lows. We dissolve 34'65 gr. of pure Copper sulphate in 200 c.c. 

 of water, mix with a solution of 173 gr. of Potassium Sodium 

 tartrate in 480 c.c. of caustic soda solution of 1*14 sp. gr. (about 

 10 per cent, soda solution), and dilute the fluid to 1000 c.c. at 15 C. 

 It remains to be mentioned that the starch contains very small 

 quantities of mineral matter. These must be determined and 

 allowed for. 



1 On other, in some respects, still more exact methods of estimating starcb , 

 see Konig, Anleitung zur Untersuchunr/ landwirthschaftl. wichtiger Stojf'e, 1891, 

 p. 231. 



112. The Occurrence of Diastase in Plants, and the Manner in 

 Which the Ferment Acts. 



Diastase is of course widely distributed in the vegetable king- 

 dom, but the quantities of diastase present in different kinds of 

 plants is by no means the same. Germinated barley is very rich 

 in diastase. If malt from a brewery is ground up in a small 

 handmill, we obtain a powder which is specially useful for the pre- 

 paration of a diastase-containing solution. We treat 25 gr. of the 

 malt powder with 100 c.c. of water, stir the mixture frequently, 

 and after some time (e.g. one to two hours) filter the solution. If we 

 add 25 c.c. of 1 percent, starch paste (prepared by mixing 100 c.c. 

 of distilled water with I gr. of potato starch, and heating to boiling 

 point) to 5 c.c. of clear diastase solution, a transformation of the 

 starch is quickly observable. Immediately after mixing the starch 

 and malt extract, a sample taken from the fluid assumes a blue 



* It must further be noted that the sugar-containing fluids, which are added 

 to the hot Fehling's solution, must not contain more than, say, J- per cent, of 

 sugar. 



