On Mr. IVcdgWDod's Pyrometer, I 5,5 



them ; or whether there be really any diiference except what 

 may aril'e from the force applied in filling the moulds in 

 which the pieces are formed, are points which we cannot 

 determine. 



However this may be, C. Gazeran, proceeding on the idea 

 of Vauquelin, has been endeavouring, and with fome fuccefs, 

 to make from the clays found in France (which contain from 

 .30 to 40 per cent, of argil) pyrometric rolls applicable to 

 Wedgwood*s fcale*. He finds the white claySAvhich con- 

 tain the largeft proportion of alumine to ainfwer beft. That 

 which he made ufc of contained in 100 parts'. 



Argil . - - 3409 



Silex -. - - 41*1 1 



Water . . - 19*25 



Lime - - - 2*30 



Oxydofiron - - 0*75 



Lofs o* 55 



Of this clay he took 150 parts by weight, which he pafled 



through a fine fieve; to this he added 6^ parts of Fontaine- 



bleau fand, wafhed and well triturated, and 200 parts of 



water. This mixture, having been flirred once a day for 



three weeks, was kneaded, for the fpace of two hours, till the 



pafte was perfectly homogeneous. It was now allowed to 



dry in the air till it had loft 170 parts out of the 200 of water 



which had been employed, and then moulded in cylinders 



made of tinned iron and of a proper fize. Tho. pafte was 



prefled in the moulds for two hours with the weight of a 



kilogram (two pounds three ounces). The pieces were then 



dried in a ftove for 24 hours in a heat of J22^ of Fahrenheit, 



and afterwards adjufted to fit zero of Wedgwood's fcale. 



Two of thefe agreeing in weight, within a centigram, with 

 thofe of Wedgwood, having been expofed with two of his to 

 a ftrong heat in a clofe crucible for an hour and a half, 

 Gazeran's indicated the temperature by one of his pieces 

 159° and by the other i5o"^, i, e, J59I °. Wedgwood's gave 

 150" and 160, I. e. 159", which is a ftriking coincidence. 



C. Gazeran obferves that Mr. Wedgwood's pyrometers 

 have frequently varied 4°, 6"", and 9° from each other, (we 



* An naif!: dr Chi mi e^ No. io6. 



V z wifh 



