108 On Ciliic ykid. 



contains different proportions of impurity, and the crystals oi' 

 soda are liable to effloresce, and thence to hold variable quan- 

 tities of the water of crystallization, neither of these is fit for 

 forming a standard by which both the buyer and seller may 

 arrive at the same estimate of the value of any given parcel of 

 juice. 



Conceiving, however, that this would be a very desirable thing, 

 I have thought of various expedients, and know of nothing which 

 would be so generally convenient for effecting this purpose as the 

 common salt f)f tartar of the shops, which, if bouglit of a re- 

 spectable chemist, will be found to be a tolerablv pure suh-car- 

 bonate of potash ; and if this be preserved in a w(dl-stop];ered 

 bottle from the action of moisture, it will be a useful test for tlit 

 purpose under consideration. 



In order to lay the foundation for a table of the quantities of 

 pure alkali which are taken up by this acid in various states of 

 concentration, I prepared some of this sub-carbonate of potash, 

 and found that 544 grains of such alkali arc required to saturate 

 one ounce avoirdupois, or 437*'^ grains of pure dry solid crystals' 

 of citric acid ; or, that one ounce and a (piarter, omitting frac- 

 tions, will render neutral one ounce of the crvstallized citric acid. 



Conceiving, however, that, for the purposes of business, a so- 

 lution of potash in ]jure water might be more generally useful 

 than the dry salt of tartar, I formed an aqueous solution of that 

 alkali, somewhat below the point of complete saturation, bv dis- 

 solving two oimces and a half of the salt of tartar in thirteen 

 ounces and a half of pure water, making in the whole one pound 

 avoirdupois, and by means of this solution* the table No. II, at 

 the end of this Essay, has been constructed. 



Notwithstanding the general certainty that must result from 

 this mode of procuring the test, it occurred to me that it would 

 be more convenient to some calico-printers to use soda. I there- 

 fore prepared some crystals of this alkali in a state of purity; and 

 having carefully abstracted the water of crystallizationf , I found 

 that 352 grains of this dry sub-carbonate of soda will accuratelv 

 saturate an avoirdupois ounce of the pure crystals of the acid of 

 lemons ; and on this result has the table been formed which is 

 marked No. III. 



* These proportions of water and alkali were chosen, in order that the so- 

 lution might be of such a strength that eight ounces of it would accurately 

 saturate as much lime-juice as should contain one ounce of pure solid crystals of 

 citric acid. The specific gravity of such a solution at GO", when filtrated, will 

 be l'I20, or 17 oz. l'.'| drachms to the wine pint. 



•f- In order to separate the water of crystallization entirely, so as to procure 

 a perfectly dry and impalpable powder of sub- carbonate of soda, it is necessai^- 

 to expose the crystals to a very gentle and long continued heat ; for when dried 

 liastily the pulverized crystals will be apt to melt in their own water of crystal- 

 lization, and become reconverted into a hard mass. 



It 



