ON THE PROCESSES FOR CLARIFYING LIQUIDS. 229 



This method of clarifying is fometimes fubject to inconve- a ffor<Js tIn »e for 

 niences, of which the principal are, that it requires much time, ta ^ t p j ace . 

 and tends by this delay to favour the formation of new pro^ 

 duels, which, by changing the compofition of the fluid itfelf, 

 no longer prefents it, independent of the abftraction of the 

 bodies which affected its clearnefs, the fame as it was before 

 its clarification. We find a very ftriking example of this kind 

 when we confider what happens in the fpontaneous clarifica- 

 tion of the juices of plants or fruits. Thefe juices when newly 

 expreffed are always turbid ; they neverthelefs become gradu- 

 ally clear ; but their nature is not then entirely the fame : they 

 contain products which would not have been found if they 

 had been clarified immediately after the expreflion. For this 

 reafon alfo it is that the juice of lemons, of goofeberries, Sec. 

 when examined before or after their fpontaneous clarification, 

 are fo different in their tafte, their colour, and their domeflic 

 utility. 



In general we may confider it as a certain fact, that all the and is not there- 

 fermentable fluids are liable by fpontaneous clarification to the fe^mSkftt* 

 effects here ftated, whereas they do not take place with re- fluids, 

 fpect to fuch liquids as are little or not at all capable of fer- 

 mentation, and of which the tranfparence is affected only by 

 the interpofition of particles incapable of acting in any manner 

 upon the conftituent parts of the fluids themfelves. 



Thus for example : Water, alcohol, ether, oil, &c. which But other fluid* 

 in their firft Hate may not have been perfectly tranfparent, are ™ cl1 » da P te * 

 may eafily become fo by fpontaneous clarification, without the m ent. 

 leait change enfuing in their compofition ; for when we exa- 

 mine them after clarification, we find them in the fame ftate 

 as other fimilar fluids which have not been fubjected to that 

 procefs. 



The fecond procefs for clarifying fluids confifb in filtering Filtration, 

 them ; but this operation can never be performed without the 

 afhftance of intermediate bodies, of which the very contracted 

 pores admit only of the palfage of the fluid, and retain all the 

 particles which were before fufpended in it. 



The inftruments of filtration are exceedingly various. Pa- Different kinds 

 per, woollen cloths, linens, cottons, carded cotton, fponge, of ^ ,ter * 

 iand, earth, pounded glafs, charcoal, porous flone, &c. all 

 thefe bodies may be ufefully employed in the prefent opera- 

 tion : 



