268 



of lime at all, but to consist entirely of chalk. To avoid 

 this risk of loss it is only necessary that the citrate of lime 

 should be brought quickly into some form of drying apparatus where 

 a temperature of from 150° to 200"" Fh. (66-93° C.) can be maintained, 

 while at the same time there is a free circulation of air through the 

 drying chamber in order to carry away the moisture. For a long time 

 the difficulty of obtaining a satisfactory and efficient drying apparatus 

 was a great stumbling block : the problem of drying the citrate of lime 

 is very similar in its nature to that of drying fruit, so th^t a good fruit 

 dryer will answer well for experimental purposes, while larger forms of 

 apparatus, worked upon the same principles, can be constructed for use 

 where the manufacture is conducted on a large scale. Where much 

 work is to be done it would appear desirable have several sets of drying 

 apparatus, so that one lot of material may be thoroughl}^ dried before 

 it becomes necessary to introduce tresh, wet citrate into the same appa- 

 ratus. Any form of apparatus in which the temperature can be main- 

 tained at from 150° to 200° Fh. or even somewhat higher, while at the 

 same time permitting sufficient ventilation to remove the moisture ra- 

 pidly, will prove efficient. It is important to lay stress on the ventilation. 

 As has been stated the proper drying of the citrate is of paramount im- 

 portance, should it remain damp, or in any way become damp from 

 careless handling, or careless storing, fermentation will speedily spoil 

 the product. 



Messrs. "Warrington and Grosjean* made an investigation of the 

 amount of water remaining in citrate of lime dried at 212° F. (100° 0.) 

 they found this to range from 5*90 to 7*68 per cent., this exists as water 

 of crystallisation ; whea dried at 392° Fh. (200° 0.) the substance con- 

 tained no water. Fermentation readily takes place if more than 

 12 per cent, of water is present, there is however no danger of 

 fermentation as soon as the proportion of water has been reduced 

 to 10 per cent, but it is desirable to continue the drying until less than 

 that amount exists : if the temperature of the drying apparatus canuot 



raised above 212° Fah. the product, as shown by the investigations 

 just referred to, may contain over 7 per cent, of water, if however the 

 drying can be finished at a higher temperature, say from 248° - 302° 

 Fah. (120 to 150° C) the proportions of water may be reduced to below 

 6 per cent. : efforts should be made to secure this thorough drying. 



When prepared in the manner described citrate of lime is a white 

 powder free from hard lumps ; when thrown into water it is easily 

 wetted and is readily diffused through the liquid on stirring. If kept 

 in a dry place it will remain good indefinitely. For shipment it should 

 be tightly packed in paper-lined barrels. It should contain over 60 

 percent, of citric acid ; a sample prepared by myself contained 65.5 

 per cent, of citric acid 2.5 per cent, of other organic acids and .5 per 

 cent, of carbonate of lime. "Warrington states that the best sample of 

 commercial citrate he has met with has contained 72 per cent, of citric 

 acid, and this is about the hightest percentage that can be reached 

 when the citrate contains no excess of chalk and has been thoroughly 

 dried. 



* Journ. Chem. Soc., Oct., 1875. 



