1821.] the Composition of Prussiates, 307 



212° Fahr. The gases were collected over mercury, and passed 

 through tubes of very small diameters to prevent too great a mix- 

 ture of atmospheric air. A portion of the gas obtained tovi^ards 

 the end of the operation was collected separately in a graduated 

 glass tube. 



No moisture condensed in the tubes, in which, for greater cer- 

 tainty, a portion of fused muriate of lime was placed, and 

 weighed with the tubes. They gained only O'OOl in weight.. 

 The gas collected in the graduated tube was examined in the 

 following manner : a small piece of caustic potash attached to a 

 very thin flexible iron wire was introduced into the tube ; lOQ 

 parts of the gas left 39*9 parts not absorbed ; so that the volume 

 of carbonic acid gas was to that of the azote as 3 : 2. This, 

 result was very diflerent from what I had expected. As no water 

 was formed in the operation, it followed, that the salt contained 

 n hydrocyanic acid. Mr. Porrett had found that the volume of 

 carbonic acid gas was four times greater than that of the azote, 

 and Dr. Thomson obtained them in the ratio of 2^ to 1. The 

 whole of the carbonic acid obtained in this experiment, absorbed 

 by a determinate quantity of potash, weighed 4- 138 grs. 



1 repeated the experiment once more, but with a stronger 

 heat, so as to soften the glass tube ; I obtained the same result, 

 but the relation of volume of th^ carbonic acid gas to that of the 

 azote then exceeded the ratio of one and a half: however, the- 

 difference was so trifling that it nliight very well be only an error 

 of observation. 



Water digested on the residuum in the tube that had 

 been exposed to heat, took up potash, and this solution gave an 

 abundant precipitate with hme-water ; the precipitate was car- 

 bonate of lime. To prove if the difference between my result 

 and that of Mr. Porrett could be caused by a bad arrangement of 

 my apparatus, I repeated the analysis of the cyanuret of mercury 

 in the same manner ; I obtained from it precisely two volumes of 

 carbonic acid gas for one volume of azote ; and on decomposing 

 another portion of cyanuret of mercury by sulphuretted hydrogen 

 gas, in a weighed glass bulb, I obtained sulphuret of mercury, 

 whose weight was to that of the cyanuret of mercury, precisely 

 as the weight of an atom of cinnabar, is to the weight of an atom, 

 of cyanuret of mercury. 



This accordance with the results obtained by M. Gay-Lussac, 

 satisfied me that the difference between my results, and those of 

 .Messrs. Porrett and Thomson cannot be attributed to my appa- 

 ratus being less suited to the purpose. 



I next repeated the same analysis with the ferruginous prus- 

 siate of barytes, previously dried at a strong heat. It gave 

 traces of moisture in the tube which conducted the gases into 

 the receiver, although its quantity was not great : 15*444 grs. of 

 the salt employed gave 0*026 of a grain of water, precisely the 

 quantity wanting, in the analysis mentioned above, to make the 



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