THE ACTION OF HEAT, ALKALIES AND ACIDS 263 



found that the most favourable concentration of the sugar solution was 20 

 per cent., that the optimum temperature was 55 C. to 60 C., the enzyme 

 being slowly destroyed at 65 C., and instantaneously at 75 C. The action 

 of invertase is greatly accelerated by minute traces of acids. O'Sullivan and 

 Thompson found that the law of mass action held for the action of invertase, 

 a result not obtained by subsequent workers until C. S. Hudson 20 showed that 

 these had neglected to take into account the mutarotation of the invert 

 sugar formed. 



Other instances of enzyme inversion that are of interest are the deteriora- 

 tion of cut cane by an invertase which, as shown by Browne, 7 is located 

 chiefly in the upper portion of the stalk, and which diffuses into the lower 

 portions of cut cane. The deterioration of stored sugars may also be properly 

 ascribed to enzymes secreted by bacteria, moulds and yeasts. In another 

 field Lewton Brain 21 showed that the fungus causing red rot of the stem 

 (Colletoirichum falcatum) also secreted an invertase causing the inversion of 

 cane sugar. 



The processes of inversion due to enzymes obey the same laws as under 

 acid inversion. In other similar biological changes this has been established 

 by Arrhenius 22 and his pupils. Here, too, temperature is a factor of im- 

 portance. The more rapid deterioration of cut cane in hot weather is well 

 known, and Browne 23 also has called attention to an increase in the deteriora- 

 tion of stored sugar in hot weather, and its almost complete cessation at 



The Inversion of Sugar in Cane Juices. The system in cane sugar manu- 

 facture when acid juices are boiled consists of sugar, neutral salts of weak 

 acids principally with a lime or potash base, and a certain amount of free 

 acid generally either sulphurous or phosphoric. The amount of free acid 

 present as indicated by analysis in a system consisting of sugar, water and 

 acid only would at a temperature of 100 C. very rapidly invert all the cane 

 sugar present. Owing, however, to the inhibitory effect of the neutral salts of 

 weak acids, or, in the language of the ionic hypothesis, to the reduction in 

 the number of hydrogen ions, very acid juices can be worked, provided the 

 acidity is due to a weak acid, such as sulphurous or phosphoric. 



The actual acidity allowable will depend on the quantity of neutral 

 salts, and this in turn will depend on the ash of the juice and on certain 

 details followed in the course of manufacture. 



If a juice is heavily limed, and the excess of lime be then neutralized 

 with sulphurous acid a neutral sulphite will be present in the juice, and 

 its presence will permit of a high acidity without inversion ; or again, as in 

 the carbonation process, in which some or all of the reducing sugars are con- 

 verted into organic acids by an excess of lime, salts of weak acids are formed, 

 which act in a similar way. This property has been used by several genera- 

 tions of Demerara and Mauritius sugar boilers in the manufacture of yellow 

 and white consumption sugars. In the former district an acidity up to 

 2 c.c. normal acid per 100 c.c. is quite usual. As indicative of actual limits 

 possible, the following experiments designed to simulate manufacturing 

 conditions were made by the writer : In the making of white and yellow 

 sugars, the use of 5 Ibs. of sulphur per 1,000 gallons of juice is excessive. 

 This quantity corresponds to the presence of 0^03 normal sulphite salt in 

 the juice. A juice was treated with lime until just alkaline to phenolphtha- 

 lein, and sodium sulphite added in quantity to correspond with the presence 



