216 THE VITAMINS 



contained small quantities of amino and amide nitrogen. The latter 

 was definitely proved to have no connection with antiscorbutic prop- 

 erties, but doubt was expressed concerning the former. Later Daubney 

 and Zilva (1926) found nickel, cobalt, and boron to be absent from 

 the ash of the concentrate and iodine to be present in amounts corre- 

 sponding to 0.1 to 0.2 milligrams per liter. This was excluded as being 

 a part of vitamin C itself, as it did not diffuse through collodion 

 membranes permeable to the active material. Phosphorus appeared to 

 be present in amounts of from 0.0005 to 0.0009 per cent of the con- 

 centrate. Later analyses by Hoyle and Zilva (1927) gave slightly 

 lower figures for phosphorus, with traces of iron and sulfur but no 

 magnesium. 



Daubney and Zilva (1926) inactivated decitrated lemon juice by 

 aeration and attempted to reactivate it by the use of various reducing 

 agents including hydrogen in the presence of platinum black, nascent 

 hydrogen obtained by the action of citric acid on magnesium, and 

 electrolysis. Nonaerated juices were subjected to the same treatment 

 and both series of samples were tested on guinea pigs. No protection 

 was secured with the aerated samples, indicating that vitamin C when 

 destroyed or inactivated by oxidation cannot be regenerated by simple 

 reduction. 



The risk of inactivation of vitamin C by excess alkalinity in the 

 precipitation with basic lead acetate led Zilva (1927) to make a study 

 of the range of hydrogen-ion activity within which the precipita- 

 tion takes place. This was found to lie between pH 5.4 and pH 

 7.2. A convenient method of bringing about the precipitation was 

 found to consist in treating the decitrated lemon juice with an excess 

 of neutral lead, centrifuging the inactive precipitate, and adjusting 

 the hydrogen-ion activity of the supernatant solution by the cautious 

 addition of dilute ammonia to pH 7.2. The fraction thus precipitated, 

 while smaller in bulk and containing much less total solids and re- 

 ducing sugar than that hitherto obtained, was of the same order of 

 activity. 



Continuing his investigation of the relationship between reducing 

 and antiscorbutic properties, Zilva (1927a) determined the reducing 

 capacity, for (toward) the indicator phenolindophenol, of various lemon 

 juice fractions with their antiscorbutic property. The two properties 

 were found to be very similar with respect to the destructive influence 

 of alkalies and of aeration, but quite unlike in their behavior toward 

 lead acetate as a precipitating agent. Only about 30 to 50 per cent of 

 the reducing substance or substances could be accounted for in the 



