Mr. Jopltng's Apparatus /or describing Curves. 235 



consist of the py-ussiate and carbonate of barytes. Since Mr. 

 Gregor's death I have examined his chemical memoranda, 

 and am thereby enabled to extract the following facts. From 

 different experiments the specific gravity of this substance 

 appears to be 1.627. Fifty grains of the coal were mixed 

 with 200 oi nitrate of barytes, reduced to powder, and placed 

 in a platina crucible, which was set in a common fire : before 

 the crucible became red hot, a violent detonation took place, 

 with the disengagement of a brilliant light and vivid heat, 

 which rendered the crucible and its cover red hot; a porous 

 light greyish mass, mixed with black streaks, remained, which 

 smelt of prussic acid. This was separated from the crucible 

 and pulverized, when it was introduced into a mattrass. Mu- 

 riatic acid operated upon the powder, and a considerable 

 quantity of an elastic fluid was disengaged. The solution 

 assumed a dark blue colour, and a very light powder was sus- 

 pended in it, resembling Prussian blue. It was poured off 

 with the fluid, and the remainder was a portion of the unde- 

 composed mineral, which, when dried, weighed 23j gi'ains. 

 This residuum was mixed with 100 grains of nitrate of ba- 

 rytes, and treated as before, when a detonation again took 

 place, but with less energy, a greyish mass remaining, which 

 was treated with muriatic acid as before : there was now no 

 blue powder separated, but the lixiviated mass became opa- 

 line. The undissolved residuum now weighed 15| grains: 

 this was again mixed with 50 grains of the nitrate of barytes ; 

 a brisk detonation and vivid flame were produced. In this 

 case the vessel was exposed to a stronger heat than before ; 

 and on the addition of muriatic acid, a blue powder was again 

 separated, when the undecomposed residue was edulcorated 

 and dried. It weighed 8j, which was mixed with 40 of the 

 nitrate, with the same phenomena, and the same separation of 

 a blue coloured powder, by the effusion of muriatic acid. 

 The residue now weighed only 2^ grains : this underwent a 

 similar treatment; and after this, as not one grain remained 

 undecomposed, it ceased to be an object of experiment. A 

 strong smell of prussic acid accompanied the detonation." — 

 Trans. Geol. Soc. of Cornwall, vol. i. p. 229. 



MK. JOPLING's apparatus FOR DESCRIBING CURVES. 



The following testimonial has been publislied of the utility 

 of an apparatus invented by Mr. J. Jopling, architect, for 

 generating Curves of several divisions of his system. 



'• Au<,'iist, 1823. 

 " We the undersigned have seen Mr. Joseph Jopling's 

 newly invented apparatus for the organical description of 



G g 2 curved 



