64 Conjiderat'ioni on Vegetalle Exira^ls, 



Ber the vegetable fiibjciSed to its aft'ton ; it forces to become 

 foluble the fubltances which \vcre not fo at a lower tempera- 

 ture ; it melts and fcparates thofe which are oily or refinous; 

 it diffipates thofe which are volatile ^ and fevcral of them it 

 combines or decompofcs. 



They expofe to the action of boiling water thofe plants or 

 parts of plants only which arc exceedingly hard, and in which 

 there exifts nothing volatile; and they often fubjeft thcfe 

 fubftances to maceration and infulion before they expofe them 

 to ebullition. 



In evaporation, the water charged with the foluble prin- 

 ciples of the vegetables gradually abandons them to unite 

 with caloric, and to form with it a volatile fluid known under 

 the name of vapour : by thcfe means, the principles before 

 diluted become concentrated, and allume confiftence, the 

 Mate and name of extracts. 



They prclcribe a gentle fire for the evaporation of the 

 juices, macerations, and infufions, and a ftronger fire for de- 

 co6lions, taking care to choofe large and (hallow evaporating 

 veffels, and to ttir the liquors to facilitate the evaporation of 

 the water, and to prevent the extraft from being burnt. 



And to prevent that alteration of which the principles of 

 vegetables, when highly diluted with water and expofed to 

 the heat of an evaporation too long continued, are fufeepti- 

 ble, they recommend to employ only the necefl'ary quantity 

 of water, paying attention to the folidity of the fubftances 

 expofed to maceration, infufion, and decoftion. They take 

 care alfo to employ for all their operations very pure water, 

 fenfible that it is only when it is in this Hate that it is fit 

 for boiling pulfe. 



During the evaporation of feveral juices or dccpAions, fome 

 phaenomena occurred which did not efcape their notice. 



They remarked, when preparing fevcral extracts which 

 they called faponaceous, that liquors became turbid ; that 

 their furface was covered with a pellicle which feparated into 

 flakes ^^'^'"e precipitated, and formed incruftations fuicepti- 

 ble of being burnt at the bottom of the evaporating velfels. 



It was Baum6 in particular who paid attention to thefe 

 precipitates; he fays they were faline. 



The preparers of fuch medicines have alfo found that, 

 during the cooling of the decoftions of roots or barks abun- 

 dant in refinous matter, and during the evaporation of fevcral 

 of thefe decoAions, precipitates more or lefs abundant were 

 formed, which, according to the opinion of Baumc, were 

 owing to the refin, more or lefs altered, of the vegetables 

 employed. 



Thcf« 



