172 Mr. Cooper on an Improved Apparatus J br [March, 



a red heat, being now introduced into the tube, its weight is to 

 be very carefully taken, which, when done, the oxide of copper 

 previously freed from its fine dust by the lawn or Cyprus sieve,* 

 and recently heated red hot, is to be poured into the tube while 

 warm, to the length of eight or ten inches, having previously put 

 into the tube as much only of perfectly cold oxide as will absorb 

 the fluid portion of matter, and about a quarter of an inch above 

 it, or to stand about the same height above the solid substance. 

 Why I recommend the present proceeding is, that a small quan- 

 tity of the cold oxide only is used to prevent the hot oxide from 

 coming in contact with the volatile matter which might other- 

 wise endanger the escape of a small portion from the tube, and 

 of course would give erroneous results; and that portion of cold 

 oxide, even if it be fully saturated with moisture, can contain 

 such a very minute quantity of water as not to sensibly affect 

 the accuracy of the analysis. Having proceeded thus far, a 

 quantity of recently ignited asbestos, or spun glass (the former 

 is best), is put into the tube, so as to occupy an inch or two, de- 

 pending on the quantity of water that is expected to be formed; 

 this must not be crammed, but put rather lightly into the tube. 

 The tube is now to be bent as represented in fig. 1, and its 

 weight may be again taken, but this is not absolutely requisite ; 

 it is, however, well to do it. The tube is then to be covered 

 with thin sheet copper, and placed between the forceps, as 

 represented in the same figure, with its open extremity inserted 

 under a jar in the ordinary mercurial pneumatic trough, or it 

 may be connected with a gasometer of Mr. Pepys's construction, 

 which, when ten or twenty grains of a substance are employed, 

 and the quantity of either carbon or azote it contains is consi- 

 derable, is convenient. Small mercurial graduated jars may be 

 used, even if very large quantities of gas are obtained, as the 

 process of decomposition may at any time be stopped almost instan- 

 taneously^ and the quantity contained in them being registered, 

 they may be alternately filled with mercury and displaced by the 

 gaseous products, as long as any comes over, reserving only the 

 last portions for examination, of which a few cubic inches alone 

 are requisite. 



The lamps being trimmed with very short wicks are now to be 

 lighted, lighting those first that are nearest the gasometer, and 

 when the tube is red hot, the remaining ones may be set fire to 

 in succession, until the whole length of tube that is filled with 

 the oxide is red hot. One set of lamps for a tube, of the size I 

 nave mentioned above, is generally sufficient, but should tubes 

 be used of larger size, such as half an inch in diameter, both sets 

 will then be required. In coating the tube with sheet copper 



• The finer portion is taken from the oxide to allow more freedom of passage for the 

 vapour through it ; in some cases the rush of gas is so sudden, was it not for this precau- 

 tion, it would be likely to burst the tube. 



+ I consider this as one of the advantages of this apparatus. 



