1826.] Scientific Notices — Chemistry, 389' 



fifths full, the rest of the space being occupied by the mercury. 

 The stoppers were then replaced as tightly as could be, the 

 bottles put into glasses in an inverted position, and mercury 

 poured round the stoppers and necks, until it rose considerably 

 above them, though not quite so high as the level of the mer- 

 cury within. Thus arranged they were put into a cupboard, 

 which happened to be dark, and were sealed up. This was 

 done on June 28, 1825, and on September 15, 1826, after a lapse 

 of fifteen months, they were examined. The seals were unbroken, 

 and the bottles found exactly as they were left, the mercury 

 still being higher on the inside than the outside. One of them 

 was taken to the mercurial trough, and part of its gaseous con- 

 tents transferred ; upon examination it proved to be common 

 air, no traces of the original mixture of oxygen and hydrogen 

 remaining in the bottle. A second was examined in the same 

 manner ; it proved to contain an explosive mixture. A portion 

 of the gas introduced into a tube with a piece of spongy platina 

 caused dull ignition of the platina ; no explosion took place, but 

 a diminution to rather less than one-half. The residue supported 

 combustion a little better than common air. It would appear, 

 therefore, that nearly a half of the mixture of oxygen and hydro- 



fen had escaped from it, and been replaced by common air. 

 he third bottle, examined in a similar manner, yielded also an 

 explosive mixture, and upon trial was found to contain nearly 

 two-fifths of a mixture of oxygen and hydrogen, the rest being 

 a very little better in oxygen than common air. 



There is no good reason for supposing that this capability of 

 escape between glass and mercury is confined to the mixture 

 here experimented with ; probably every other gas, having no 

 action on the mercury or the glass, would have made its way out 

 in the same manner. There is every reason for believing that a 

 small quantity of grease round the stoppers would have made 

 them perfectly tight. — (Journ. of Science.) 



2. Cafein, 



M. Garot adopts the following method of preparing this sub- 

 stance : — A quantity of bruised raw coffee was twice infused in 

 boiling water : the brown liquors, when cold, were mixed ; on 

 the addition of a solution of acetate of lead, a very abundant 

 precipitate of a pistacio green colour was obtained. The liquor 

 after filtration was yellowish, but after separating the excess of 

 acetate of lead by means of sulphuretted hydrogen, it became 

 nearly colourless ; the free acid remaining in solution was satu- 

 rated by ammonia, and by careful evaporation, crystals of cafein 

 are obtained, which, by purification, were procured in colourless 

 silky crystals. It appears by these experiments, that the colour- 

 ing and extractive matter of the coffee are precipitated by the 



