250 



liquor effervesces with more whiting, or the precipitate effervesces 

 with more juice. The amount of unneutralised acid is about l-2£ p. c. 

 of the original acidity of the juice. Pure citric acid is readily 

 neutralised by whiting, malic und aconitic acid are not ; the 

 final acidity is thus possibly due to the presence of these acids. Citric 

 acid, however, is not neutralised by chalk if phosphates, and especially 

 ferric phosphates, be present ; this fact will also explain the result. 

 It is not advisable to neutralise completely by the use of lime, as vege- 

 table impurities are then thrown down which are afterwards difficult 

 to separate. 



The precipitated calcium citrate is washed with hot water on a filter. 

 It is next brought by the addiiion of water to the state of thin cream, 

 and decomposed, with constant agitation, by the addition of a small 

 excess of sulphuric acid (sp. gr. 1.7.). The occurrence of an axcess of 

 sulphuric acid is known by the liquor affording a precipitate with a 

 strong solution of calcium chloride after some minutes' standing. 



The citric acid liquor is then separated from the gypsum, which is 

 washed on a filter. The liquor is evaporated in shallow leaden baths 

 by steam heat. Much gypsum is at first deposited, from this clear 

 liquor is run off and further concentrated. When strong enough to 

 crystalise, the h< t liquor is run into a wooden tub provided with an 

 agitalor, and the liquor is kept in constant motion while cooling; by 

 this pre cess, known as "granulation," the citric acid is obtained 

 as a crystalline powder. The mother liquor is again concentrated, and 

 salt again obtained by granulation. The process may be repeated a 

 third time. The liquor is then too dark and impure for further crystal- 

 lisation, and is known as 'old liquor.' The granulated citric acid when 

 drain, and if necessary slightly washed, is redissolved, decolourised by 

 heating with animal chaicoal (previously freed from phosphates by 

 hydrochloric acid again concentrated to the crystallising point, and 

 poured into leaden trays about 3 inches deep ; the crystals here formed 

 are the citric acid of commerce. Citric acid thus prepared always con- 

 tains a trace of lead. 



The 'old liquor' is diluted wiih water, and the citric acid it contains 

 precipitated with an excess of whiting, exactly as in the case of the 

 original juice. The liquor is never neutralist d by the whiting; this 

 may be either due to aconitic acid formed during the heating of the 

 citric acid liquors, or to the presence of ferric or aluminic phosphate 

 derivtd from the whiting. 



.Any considerable excess of sulphuric acid in ihe liquors, or any over- 

 neating, must be avoided, as occasioning decomposition of citric acid. 

 The presence of iron or aluminium in the whiting also occasions loss, 

 as citric acid holding iron or aluminium in solution is not precipitated 

 by Cidcium car bom te. In consequence of the non-precipitation of iron 

 or aluminium from citric solutions by whiting, the citric liquors of the 

 factory remain nearly lure, however long the work may have been con- 

 tinued, a result very different from what happens in the case of 

 tartaric acid ; the purity of citric acid liquors is however obtained at the 

 expense of some loss of citric acid. In a well-conducted factory the 

 total loss during manufacture will amtunt to 12-15 p. c. of the citric 

 acid in the juice. 



The total quantity of citric acid made in the Uruted Kingdom in 



