4 Historical Sketch of Improvetnents in [July, 



. page of the Annals of Pliilosophi/ just quoted. I have no doubt 

 that this apparatus furnishes an important addition to the means 

 of analysis. It is a considerable simplification of Berzelius's 

 original contrivance for the same purpose ; while the small size 

 of I lie tube renders the quantity of common air which can be 

 mixed with the gas exceedingly trifling. 



The apparatus which I myself use for similar experiments is 

 fully as simple as that of Dr. Prout, and I consider it as possess- 

 ing some advantages to those persons who are in possession of a 

 mercurial trough of a sufficient size to admit experiments to be 

 made over mercury on a tolerably large scale. It consists of 

 three tubes, all fitted to each other by grinding. The first, 

 which is of copper, is about 12 inches long, and the third of an 

 inch in diameter. The second is of brass ; its internal diameter 

 does not exceed the tenth part of an inch, and it is about four 

 inches in length. It is fitted by grinding to the open end of the 

 copper tube. The third tube is of glass with a brass cape on one 

 end to which the other extremity of the brass tube is fitted by- 

 grinding. This glass tube is about 

 eight inches long, and its diameter is c 

 about 0-4 inch. The figure in the 

 margin will give the reader some idea 

 of the arrangement of these tubes. A 

 ' is the copper tube, B the brass tube, 

 and C the glass tube. The glass tube 

 . is filled before the process with muriate 

 of lime well-dried, and the weight of it is carefully taken. The 

 tube A is put into a small chotfer which is filled with red-hot 

 ■ieharcoal. The furthest extremity of the tube C is plunged under 

 a graduated jar inverted over the mercurial trough and filled with 

 mercury. Sometimes it is necessary to expose the tube A to a 

 strong heat : this is easily done by blowing the charcoal with a 

 ". pair of bellows. Sometimes it is necessary to keep the substance 

 -subjected to analysis quite cold till the greater part of the tube 

 A is red hot. This I accomplish by introducing the mixture of 

 the peroxide of copper, and the substance to be analyzed into 

 ■ the bottom of the tube A, so that it shall occupy not more than 

 three inches of the length of the tube. This portion is coated 

 with wet clay, and drawn entirely beyond the choffer, that portion 

 of charcoal Avhich is furthest removed from the coated part of 

 ' tlxe tube is first kindled, and the heat is allowed to penetrate 

 very slowly to the coated part of the tube. When about four or 

 five inches of the copper tube have become completely red-hot, 

 the clay coating is removed from the tube; the heat soon makes 

 . its way to the furthest end of the tube, and in a few minutes gas 

 .begins to make its appearance. If the substance subjected to 

 '•analysis be very volatile (camphor, for ex?,mple), it is merely 

 -. necessary to allow the apparatus to remain for about a quarter 

 of an hour to obtaii:s its complete decomposition and conversion 



