1 68 Process for extracting the Salt 



Continue this evaporation, filtration, and washing, until 

 the hquor, by means ot" a gentle heat, has been brought to 

 half the consistence of syrup. Then pour the liquid into a 

 vessel of earthen ware *, which must be deposited in a cool 

 place and left at rest for a fortnight. 



At the end of that time pour off, by inclining the vessel, 

 the condensed liquor, whicii will float over the cr)'stals 

 that have been formed. Wash them with a suificient quan- 

 tity of water, rubbing them gently with a small soft brush, 

 or the barb of a quill, in order to free them from the thick 

 extract which adheres to them. 



After this washing, detach the crj'stals, removing as little 

 as possible the rcsino-extractive matter to which they are 

 often fixed in this first crystallization f. Pound the salt and 

 dissolve it, triturating it several times in a sufficient quantity 

 of cold water. Filter these solutions, including the liquor 

 vhich arises from the washing of the crystals, and evaporate 

 the wdiole to the consistence proper for crystallization %• 



By this first piu'ification you will obtain crystals very 

 little coloured, and much less mixed with substances foreign 

 to the salt. If you wish to obtain them of a greater degree 

 of purity, you must proceed to a second purification in the 

 following manner ; 



After having washed and detached the crystals, dissolve 

 them cold as before ; filter the liquid, wash the deposit, 

 and reduce the whole by slow evaporation to the proper 

 degree. 



The salt obtained will be exceedingly beautiful and per- 

 fectly pure. Its crystals are formed of lamina truncated 



* For these crystallizations I prefer flat dishes to those which are 

 conical. 



f If care has been taken to filter the liquor several times, accord- 

 ing as it is concentrated, and always after it has been suffered to cool, 

 it will be so much freed from the resino-gummy part, that after the 

 first crystallization^ though the saline mass will still be of a russet colour, 

 the base of the crystals will be free from that matter which it was my 

 chief object to remove. 



The small portion of salt which I had the pleasure of sending to you 

 arose from tlic first crvstallization alone. When the infusion was reduced 

 to six or seven pinf^, I took care in th* courscof the subsequent evapora- 

 tion to filter it cold at three diffti ent times. By pursuing th.is course, very 

 little matter adheres to the saline crus'r, and the supernatant extractive 

 niattcr can be separated with the greater facility. 



J The more I advanced in tlic purification of my salt, the less I thick- 

 ened the liquor: the degree of concentration must he proportioned to the 

 quantity of extractive or resino-mucous matter it may have contained. It 

 is not easy to hit this point. 



at 



