294 PRACTICAL PHYSIOLOGY 



Preparation of Solutions. Solution I. 12'5 gr. CuSO 4 (purified as directed in the 

 footnote 1 ) are dissolved by heat in 75 c.c. water and the solution cooled to 25 C. 

 In a large porcelain basin 250*0 gr. potassium carbonate, 200 '0 gr. potassium 

 sulphocyanide and 50-0 gr. potassium bicarbonate are dissolved by stirring in 

 600 c.c. water. During the process of solution of these salts the temperature 

 at first rises and then falls. If the potassium bicarbonate does not become 

 dissolved the basin must be placed on a water bath and the temperature 

 raised to 40 C. (but no higher). The solution is then cooled to 15 C. and the 

 copper solution mixed with it in small quantities at a time with frequent 

 shaking, so as to prevent any large amount of precipitate forming. The 

 solution is then made up to 1 litre in volume. 



Solution II. 6 "55 gr. hydroxylamin sulphate or 5*56 gr. hydroxylamin chloride 2 

 is dissolved in water and the solution added to one of 200 gr. potassium sulpho- 

 cyanide in 1500 c.c. water. The volume is then brought up at 2000 c.c. 



Titration. The amount of sugar added must be less than 0'06 gr. (to which 

 limit the table has been constructed). If, therefore, the solution to be examined 

 contain less than 0-6 per cent., 10 c.c. of it are taken for the estimation ; if it 

 contain more, then such a number of c.c. must be taken as will yield a total 

 amount less than 0-06 gr. In all cases the sugar solution must be made up to 

 10 c.c. 3 



Mix the 10 c.c. sugar solution with 50 c.c. of the copper solution in an 

 Erlenmeyer flask. Place on wire gauze over a Bunsen burner and bring to the 

 boil. Maintain the boiling for exactly three minutes. Cool the solution 

 quickly by holding the flask under the cold water tap. Place under a burette 

 containing the hydroxylamin solution, and add this, with constant shaking 

 of the flask until the blue colour is just discharged. 



The weight of dextrose corresponding to the amount of hydroxylamin 

 solution used is then read off on the following table. (See p. 295.) 



Pentoses. 



Besides the hexoses, animal tissues also contain small amounts of pentoses, 

 that is, sugars containing five carbon atoms, C 5 H 10 5 . Being aldehydic in nature, 

 they possess reducing powers and form osazone crystals. They do not ferment 

 with pure yeast, but they all rotate the plane of polarised light. In the animal 

 tissues pentoses do not exist in a free state, being, as far as is known, bound 

 to guanylic acid (see p. 310). They are very plentiful in plants, where they 



1 Filter a hot saturated solution of copper sulphate into a large evaporating 

 dish, and after covering with a sheet of filtered paper allow to stand for some 

 hours. Collect the crystals which separate out on a filter, and after all the mother 

 liquor has drained, open up the filter and spread out the crystals between several 

 folds of filter paper. Press then between the folds of filter paper, removing them 

 to fresh paper, until perfectly dry. This is ascertained by placing a glass rod on 

 the crystals and then tapping it. If dry no crystals will stick to the rod. 



2 The sulphate is recommended by Bang, but we have found the chloride 

 quite as suitable. 



3 Where there is no previous knowledge as to the strength of the sugar 

 solution a preliminary titration should be made by boiling 10 c.c. of the 

 solution with 50 c.c. of the copper solution for three minutes. If the blue 

 colour disappears, repeat with 5 c.c., and so on until the amount is found 

 which does not discharge the blue. 



