294 VEGETABLE SUBSTANCES. 



of sugar, water, extractive matter, and mucilage. 

 These considerations caused it to be a matter of great 

 interest with chemists to discover some method 

 whereby this valuable acid might be separated and 

 preserved in a state of perfect purity. 



Alcohol was added by Scheele and other practical 

 men, with the intention of precipitating the muci- 

 lage ; but this preserved it very imperfectly, for 

 although the mucilage was separated thereby, the 

 extractive matter and the sugar were still held in 

 combination. In 1774 M. Georgius, a Swedish 

 chemist, published a process for separating the mu- 

 cilage and concentrating the acid. The method pro- 

 posed was to keep the lemon juice for a long time in 

 a cool place in inverted bottles, and then expose it to 

 a temperature below the freezing point of water. 

 The water with the mucilage freezes, and this frozen 

 portion is repeatedly removed, until at length the 

 juice is reduced to one-eighth of its original quan- 

 tity. It must not, however, be exposed to too intense 

 a cold, lest part of the acid should also congeal with 

 the aqueous portion ; the temperature should there- 

 fore not be lower than 28 Fahrenheit. By this 

 management none of the acid is lost, and when con- 

 centrated and purified, it may be kept, for many 

 years without sustaining any injury. This is at 

 best but a very tedious process, which could not be 

 easily practised in countries where the fruit grows, 

 as the cold there would never be sufficiently intense*. 

 The juice, after being subjected to this process, still 

 has the extractive matter combined with it, and this 

 prevents its crystallizing. The method was there- 



* As far as regards Sicily and Naples, recourse might be had 

 to ice, or rather congealed snow, which is preserved all the year 

 round in caves or pits dug for the purpose on Etna, and most of 

 the high mountains of that kingdom. But the whole process is 

 perhaps too artificial for those parts, and, after all, is defective. 



