54 On C'Uric ylcid* 



acid may at any time be produced*, and if the. fii'st solution of 

 the brown crystals be passed through a skin of wash-leather, 

 stretched upon a frame, so much of the colouring matter will be 

 abstracted that two or three solutions in clear water will be suffi- 

 cient to give crystals of the desired purity. 



There is another point respecting the conducting of this busi- 

 ness which deserves our notice, and that is the management of 

 the mother-waters. In the manufacture of every kind of salt, 

 the profit very much depends upon the oeconomy which is ob- 

 served in reducing these to a solid or a marketable form. But in 

 this article, the high value of the crystals, and the pecuHar difli- 

 culties attendant on the reduction of tliese residuary lii|Uors, 

 render this part of the subject important to those who operate 

 on a large scale. Whenever this acid is first boiled to a suffi- 

 cient strength for crystallization, the small excess of sulphuric 

 acid carbonizes a portion either of the acid or the mucilage; 

 and therefore, when several parcels of juice have been concen- 

 trated, there will be a considerable quantity of very black un- 

 crystallizable mother-liquor. This kind of residuum has given 

 much trouble to some operators, and it has often been thrown 

 away as useless. By the following management, however, the 

 whole of the citric acid which it contains may be turned to a 

 good account, and produce fair and clean crystals. The process 

 is as follows : 



Whatever the quantity of mother-liquor may be, let it be di- 

 luted with ten or twelve times its measure of pure water, arid the 

 water intimately mixed with it. Then add whiting to it, by 

 degrees, till it is completely saturated, and proceed with it in all 

 respects as before directed, and as if it were fresh lemon juice. 

 Here it will be necessary to wash the product of citrate of lime 

 with several successive portions of water ; and if this be attended 

 to, the crop of crystals which it will yield will be as fine as any 

 before obtained. 



On referring to my notes, while operating on some large par- 

 cels of lime-juice, I find the following entry, which is given in 

 the hope that it may furnish some useful hints to those who have 

 had less practical experience, and enable them to avoid some 

 errors into which I had fallen before I had that knowledge of the 

 process which I have since acquired. Three casks of lime-juice, 

 which measured together 270 gallons, were drawn off into a 

 large wooden vessel ; and to this were added 118 lbs. of best 

 whiting, which completely saturated it. When the citrate of 

 lime had precipitated, the supernatant liquor was taken away 



« Though the first product maybe in needle-shaped crystals, the acid when 

 further purified will always appear ia rhomboidal prisms. 



and 



