288 PHILOSOPHICAL TRANSACTIONS. [ANNO 1 782. 



A piece of an Etruscan vase melted completely at 33°; pieces of some other 

 vases and Roman ware about 36°; Worcester china vitrified at 94 ; Mr. Spri- 

 mont's Chelsea china at 105°; the Derby at 1 12°; and Bow at 121°; but Bristol 

 china showed no appearance of vitrification at 135°. The common sort of 

 Chinese porcelain does not perfectly vitrify by any fire I could produce; but 

 began to soften about 120°, and at 156° became so soft as to sink down, and 

 apply itself close on a very irregular surface underneath. The true stone nan- 

 keen, by this strong heat, does not soften in the least; nor does it even acquire a 

 porcelain texture, the unglazed parts continuing in such a state as to imbibe water 

 and stick to the tongue. The Dresden porcelain is more refractory than the 

 common Chinese, but not equally so with the stone nankeen. The cream- 

 coloured or queen's ware bears the same heat as the Dresden, and the body is as 

 little affected by this intense degree of fire. 



Mr. Pott says, that to melt a mixture of chalk and clay in certain proportions, 

 which proportions appear from his tables to be equal parts, is " among the 

 master-pieces of art." This mixture melts into a perfect glass at 123° of this 

 thermometer. The whole of Mr. Pott's or any other experiments may, by 

 repeating and accompanying them with these thermometric pieces, have their 

 respective degrees of heat ascertained, and thereby be rendered more intelligible 

 and useful, to the reader, the experimenter, and the working artist. I flatter 

 myself that a field is thus opened for a new kind of thermometrical inquiries; 

 and that we shall obtain clearer ideas with regard to the differences of the degrees 

 of strong fire, and their corresponding effects on natural and artificial bodies; 

 those degrees being now rendered accurately measurable, and comparable with 

 each other, equally with the lower degrees of heat which are the province of the 

 common mercurial thermometer. 



Appendix. Analysis of the clay of which the thermometric pieces are formed. — 

 This clay makes no effervescence with acids. Diluted nitrous and marine acids 

 being boiled on it, and afterwards saturated with fixed alkali, no precipitation or 

 turbidness appeared. It therefore contains no calcareous earth, as that earth 

 would have been dissolved by the acids, and precipitated from them by the 

 alkali. Calcined with powdered charcoal, it contracted no sulphureous smell, 

 and the acids had no more action on it than before. It therefore contains no 

 gypsous matter, or combination of calcareous earth with vitriolic acid; as that 

 acid would have formed sulphur with the inflammable principle of the charcoal, 

 and left the calcareous earth pure, or in a state of solubility by acids. 



Some of the clay was calcined with an equal weight of salt of tartar, which, 

 for the greater certainty in regard to its purity, had been run per deliquium, 

 and afterwards evaporated to dryness. The calcined mixture was boiled in water, 

 the filtered liquor slowly evaporated, and suffered to cool at intervals. No 



