1823.] 



On Vegetable and Animal Substances. 



345 



tice introduces a similar fallacy to that above described 



The plan which I adopt for the purpose of desiccation seems to 

 answer very well. Having put the pulverulent animal or vege- 

 table matter into short phials, furnished with ground glass stop- 

 pers, I place the open phials in a large quantity of sand heated 

 to 212° F. in a porcelain capsule, and set this over a surface 

 of sulphuric acid in an exhausted receiver. After an hour or 

 more, the receiver is removed, and the phials instantly stopped. 

 The loss of weight shows the total moisture which each of them 

 lias parted with ; while the subsequent increase of their weight, 

 after leaving them unstopped for some time in the open air, indi- 

 cates the amount of the hygrometric absorption. This is conse- 

 quently the quantity to be deducted in calculating experimental 

 results." 



" Many chemists, particularly in this country, have employed 

 the heat of a spirit-lamp, instead of that produced by the com- 

 bustion of charcoal, for igniting the tube in which the mixed 

 materials are placed. I have compared very carefully both 

 methods of heating, and find that for many bodies, such as coal, 

 and resin, which abound in carbon, the flame of the lamp is 

 insufficient; while its application being confined at once to a 

 small portion of the tube, that uniform ignition of the whole, 

 desirable towards the close of the experiment, cannot be 

 obtained.* I was hence led to contrive a peculiar form of fur- 

 nace, in which, with a handful of charcoal, reduced to bits about 

 the size of small filberts, an experiment may be completed with- 

 out anxiety or trouble, in the space of half an hour. Since I 

 have operated with this instrument, the results on the same body 

 have been much more consistent than those previously obtained 

 with the lamp ; and it is so convenient that I have sometimes 

 finished eight experiments in a day." 



Dr. Ure next gives a particular account of the whole appara- 

 tus he employs, illustrated with an engraving. " Fig. 1 is an 



horizontal section of the furnace, in which we perceive a semi- 

 cylinder of thin sheet iron, about eight inches long, and three 



* Some remarks, by Dr. Prout, on the relative accuracy of analyses performed by 

 means of the charcoal ami of the lamp apparatus, will be found in the Annals for Dec. 

 last, p. 425 Edit. 



