56 On Citric Jcid, 



the oil of vitriol is not sufficiently diluted before it be employed. 

 Indeed, from the last operations which I superintended, I am 

 led to believe that it cannot be oeconoaiical to use this acid in a 

 higher state of concentration than one part of the suiphuric acid 

 of commerce to six parts of water. Tiie whole quantities used, 

 were lime-juice 720 gallons, carbonate of lime 267 lbs., sulphuric 

 acid 240 lbs., water (besides the quantity which was before ia 

 the nitrate of lime *) 75G lbs. 



Several other parcels of citrate of lime were afterwards treated 

 with sulphuric acid properly dihited, and these inconveniences 

 avoided ; but it is not in my power to furnish the amount of the 

 crystals that were produced from any of these parcels, as I dis- 

 posed of my share oT the whole of the citric acid in a state of 

 solution, and the task of concentrating it for crystallization fell 

 into other hands. 



From other experiments, i^owever, I have reason to conclude 

 that 20 gallons of good juice will generally give 18 lbs. of dry 

 citrate of lime, and that if the v. hole process be well conducted, 

 these IS pounds of citrate will furnish 10 pounds of good white 

 crystals of citric acidf. 



A different metiiod h.as been proposed by Richter for pro- 

 curing the crystallized citric acid ; and the author of the process 

 says (Mr. J. Thomson's Notes to Fourcroy) that the crystals 

 produced in this way are much finer than those which are fur- 

 nished by the old method. It consists in saturating lemon-juice 

 with potash, and in adding to the hltrated solution, a solution of 

 acetate of lead so long as any white precipitate continues to be 

 formed. 



In this process the citric acid unites of course to the metal, 

 and the acetic acid with the alkali. The citrate of lead, after 

 being well washed with water, to separate any of the acetate 

 which may adhere to it, is to be digested with a sufficient quantity 

 of diluted sulphuric acid, and stirred frequently. During this 

 digestion sulphate of lead is formed, and the disengaged citric 

 acid exists in the supernatant liquor. By evaporating this with 

 a gentle heat, beautiful crj-stals of citric acid will be fornied. 



As the citric acid takes the lead directly from the acetous 

 acid, the citrate of lead may be obtained by adding lemon-juice 

 to the acetate or lead. But the mucilage and other impurities 



• If the ci'rate be trcared with oil of vitriol immediately after it has been 

 washed, as is frequently the case, a dilution of three parts of water to one part 

 of oil of vitriol may be sufficient, as there will be much water in a state of mix- 

 ture with the citrate of I'me, 



f It has been stated that " the quantity of solid citric acid iu a g^allon of lime- 

 juice varies from 14 to 18 ounces." I confess, however, that I have not been 

 able to procure tliis proportion from any of the parcels on which 1 operated. 



are 



