1826.] M. Pelletier on Cafein, 355 



Hitherto but little is known about cafein, M. Robiquet 

 not having published his memoir upon it, and we were waiting 

 its publication in order to state some observations which had 

 been made by us only.* 



Having some time since had occasion to prepare a quantity of 

 cafein, I employed a process which appeared to combine 

 several advantages, and this, I think it proper to publish, more 

 especially because I had, rather from analogy than certain proof, 

 hazarded the opinion, in opposition to that of M. Robiquet's, 

 that cafein is alkaline ; and I have since satisfied myself that 

 with acids it acts similarly to those substances which are electro- 

 chemically indifferent, and that when it dissolves in acids, the 

 solution takes place like that of narcotin for example, that is, 

 without saturating the acid, and very differently from morphia, 

 See. ; and I, therefore, take advantage of this opportunity to 

 state what appears to me to be fact in this respect. 



M. Robiquet obtains cafein by treating raw coffee with cold 

 distilled water ; the brownish liquors are evaporated after being 

 treated with calcined magnesia ; and then being suffered to 

 remain, the cafein crystallizes in nearly colourless semitransparent 

 arborescent crystals. It is purified by solution in alcohol or 

 boiling water, from which it separates on cooling in silky crys- 

 tals resembhng amianthus. The process adopted by M.Caventou 

 and myself is rather different : we exhaust the raw coffee by 

 alcohol, the spirituous extract is afterwards treated by cold 

 water which separates a fatty matter; the solution of the 

 extractive matter is heated with the addition of caustic mag- 

 nesia; the magnesian precipitate collected in a filter is sHghtly 

 washed and treated with alcohol to separate the cafein, which is 

 separated by evaporating the alcohol. 



A difficulty occurs in the evaporation if the magnesian preci- 

 pitate is insufficiently washed, and the cafein extracted by the 

 alcohol is rendered impure by the presence of adventitious 

 colouring substances resembling syrup ; and from these it is 

 very difficult to purify it wif^hout incurring great loss; on the 

 other hand, if the precipitattz is well washed, very little cafein is 

 obtained, it being carried off by the washing water. It is 

 indeed true, that by concentrating the washings and putting 

 them in a cold place, crystals of cafein may be procured ; but 

 this does not always succeed, esjiecially in summer, owing to 

 the fermentation which takes place in the hquors. It is to avoid 

 this inconvenience that I have sought for an expeditious method 

 of separating the cafein from the washing water. I wash the 

 magnesian precipitate perfectly to dissolve the whole of the 



• An extract of M. Robiquet's memoir will be found in the Dictionnaire Technolo- 

 guique. Article Cafe ; and of ours in the Dictionnaire de Medicine. 



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