and of some of its Compounds, 117 



We observe here a difference of 2 per cent, of carbon, which 

 M. Pay en has obtained over the results of the above-men- 

 tioned chemists. 



In order to elucidate this discfTepancyy Dr. Hofmann in- 

 duced me to make some experiments under his direction, 

 partly m ith a quantity of beautiful caffein \vhich he gave me* 

 and partly with a specimen which I have prepared myself. 



Caffein, 



To ensure perfect purity of the substance it was crystal- 

 lized three times from dilute alcohol, washed and dried. Thus 

 purified, it formed very beautiful long white prisms, perfectly 

 transparent when dried in the air, but which became opake 

 if exposed to a higher temperature. The crystals dried in the 

 water-bath lost no weight when kept in an air-bath for four 

 hours at a temperature of 130° C. 



The specimen which I had prepared myself was obtained 

 from Costa Rico coffee, by boiling the bruised fruit in water, 

 precipitating the decoctions by basic acetate of lead and treat- 

 ing the filtrate with hydrosulphuric acid ; after the whole of 

 the lead had been removed, I evaporated the liquid to dry- 

 ness in a water-bath, in order to get rid of acetic acid, and 

 dissolved the residue in a small quantity of boiling water : 

 upon cooling, the caffein crystallized out of a dark colour, 

 and very impure. To purify it, it was washed and recrystal- 

 lized three times from water, and finally from alcohol. It was 

 then perfectly white, and had exactly the same appearance as 

 the specimen which I obtained from Dr. Hofmann. 



Analysis. 



I. 0*3827 grm. of substance, dried at 100° C. and burnt 

 with chromate of lead, gave 0*6948 grm. of carbonic acid, and 

 0'1800 grm. of water. 



II. 0*417 grm. of substance, burnt with chromate of lead 

 and chlorate of potash, gave 0*7552 grm. of carbonic acid, 

 and 0*1965 grm. of water. 



III. 0*3934 grm. of substance of my own preparation gave 

 0*7123 grm. of carbonic acid and 0*1878 grm. of water, which 

 calculated in 100 parts gives — 



I. II. III. 



Carbon . . . 49*51 49*39 49*37 



Hydrogen . . 5*22 5*23 5*30 



* I owe this specimen, of great beauty, to the well-known kindness of 

 Mr. E. Merck of Darmstadt.— A. W. H. 



