104 . On Citric Acid. 



buy lemon-juice for themselves, and use it in different states of 

 concentration, according to the nature of the processes to which 

 it is to be adapted. 



For most of the styles of work in which citric acid is employed, 

 they find that the common impurities in lemon-juice are of verv 

 little consequence ; and that when the juice itself has undergone 

 no other process than that of being concentrated by evaporation, 

 it very well answers their purpose, and supersedes the use of the 

 crystallized acid. 



y\.s there is always abundance of spare heat in every large ca- 

 lico-print work, the process of evaporation may be conducted at 

 no expense ; and if it be continued very slowly for some con- 

 siderable time, the acid will be sufficiently concentrated, and 

 this without waste. For when the evaporation is thus managed, 

 the vapour which arises will carry off none of the acid; and when 

 it arrives at a certain point of concentration most of the muci- 

 lage will be separated, one part of which generally rises to the 

 surface, and the other precipitates. 



It is time, however, to come to the particular point which 

 first induced me to think of writing on this subject, namely, the 

 knowledge of this circumstance, that the printers depend solely 

 on the hydrometer for ascertaining the goodness of lemon-juice, 

 which made me very desirous of recommending to them some 

 less fallacious guide. 



Various reasons may be adduced to show the uncertainty of 

 the hydrometer, but one or two will suffice. It is possible, for 

 instance, that two parcels of juice may appear to differ very much 

 when examined by the hydrometrical test, from the difference of 

 the quantity of mucilage, though the same parcels may be of 

 equal goodness as to the produce of the crystals, or real acid 

 that may be procured from them. In like manner, a pipe of 

 lemon-juice may be sophisticated with other acids, so as to make 

 it pass the hydrometer, and yet be worth little for the printer's 

 use. 



On these accounts it appears to me that there can be no safety 

 in purchasing this article, unless the buyer avail himself of the 

 use of chemical tests *. 



Whenever, thereforfi, a parcel of lemon-juice is offered for 

 pale, the first thing should be to take its specific gravity by the 

 hydrometer, or by a gravity bottle, and note that down. Should 

 it prove to be only of the specific gravity of about 1'0156, which 

 is 16 ounces 4 drachms to the wine pint, it may at once be re- 

 jected as not worth purchasing ; for, good juice varies from a 



* An experienced calico-printer has assured mc that fine wheat flour is some- 

 times employed to adulterate lemon-juice. It certainly may be so incorporated 

 wilii the mucilage as to afl'ect the hydrorTieter cons-idcrably. 



specific 



