264 CHAPTER XIII 



of o»oi, 0-02 and 0-03 normal sulphite salt per 100 c.c. of juice. Phosphoric 

 acid was then placed in the samples and the acidity determined by the 

 routine methods of analysis. The prepared juices were then heated at a 

 temperature of 97°-98° C for 30 minutes and examined, to determine when 

 inversion occurred. With concentrations of sodium sulphite •01,0-02 and 

 0-03, normal inversion was detected when the concentration of the phos- 

 phoric acid was 2-4, 4-2 and 6-8 normal per 100 c.c. of juice respectively. 

 This experiment indicates that under the usual processes there is a very 

 considerable margin of safety in boiling acid juices before any loss due to 

 inversion occurs. 



The Effect of Higher Temperatures on Cane Sugar. — Cane sugar at tem- 

 peratures as low as 40° C. suffers some change and caramelization, as has been 

 shown by Bates and Jackson^* in their studies on the preparation of a pure 

 sugar for a polariscopic standard. The destruction is, however, very small, 

 and has no bearing on manufacturing losses. 



The original investigation on the effect of high temperatures was made 

 by PeUet^^, and the results most often quoted are those of Herzfeld^", and 

 the subject has been studied later by HazewinkeP', Douschsky^^, Zu^ew^' 

 Pokomy^" .Deerr^i and others, mainly in connection with the extended 

 appHcation of the pre-evaporator. Some of Herzfeld's results in which 

 sugar solutions with an alkalinity of o-oi to 0-05 per cent, were heated in 

 metal containers are given below, the figures referring to the sugar destroyed 

 in one hour as a percentage on the sugar originally present. The solutions 

 were made alkaline to inhibit the secondary action of the acids formed from 

 the sugar, which would be much greater than that due to heat alone. 



Evidently between 120° C and 130" C the rate of destruction increases 

 very rapidly. 



It is to be noted that these results were obtained in the presence of 

 small quantities of alkalies. The products of the decomposition of sugar 

 are acid, and hence on continued heating two factors are at work, the con- 

 tinued breakdown of the sugar molecule and the inversion of the sugar by 

 the acid formed. This last factor becomes active only when the free alkali 

 has been neutralized and even then the salt formed continues to exert 

 its inhibitory action, as explained in a previous section. 



In experiments made by the writer it was found that the nitrates, halides, 

 and sulphates of the alkahes and alkaline earths accelerated the rate of 

 destruction of sugar at higher temperatures, salts of weaker acids retard- 

 ing the rate. 



In cane juices, as explained in a previous section, the quantity of neutral 

 salts and acids is variable. To determine what should be the safe acidity 

 at which juices could be heated in a pre-evaporator, the writer made the 

 following experiment : — Defecated cane juice of an acidity 0-5 normal was 

 reduced to the acidities shown in the annexed table by the addition of either 

 caustic soda or of oxalic acid. Oxalic acid was selected for use, as a 



