357 



Another experiment was made on one of those varieties of the 

 opal which are known by the names hydrophones, changeable opal, and 

 oculus inundi, which, besides possessing the remarkable property of 

 becoming transparent in water, and other Maids, are eminently 

 distinguished by manifesting, in that situation, the beautiful play, 

 or change of colours, peculiar to the opal. This analysis was made, 

 under those circumstances, which were calculated to yield some 

 knowledge of the nature of those constituent parts, which had been 

 dissipated, without examination, in the two experiments just men- 

 tioned ; and therefore is the experiment, on which we might, almost, 

 be allowed to depend the decision of the question whether any 

 thing of a bituminous nature enters into the composition of the opal. 

 The result of this experiment is strongly affirmative of this fact; 

 and, indeed, seems to confirm the opinion I have ventured to ad- 

 vance, in a most striking manner. You must have perceived that I 

 have been regularly led on to the supposition of the presence of 

 bitumen in opal, by first noticing the impregnation of bituminous 

 wood with silex, by which was formed silicized bituminous wood ; 

 then tracing this into the opalized wood and the pitch-stone ; thence 

 to the semi-opal, and at the last to the opal itself: you will there- 

 fore readily conceive the satisfaction yielded by the analysis made 

 bv Mr. Klaproth, which afforded a u result at once so unexpected 

 and decisive ; and so precisely accordant with the experiments of 

 Mr. Pepys, on opaline wood'. 



One hundred grains of the hydrophanous opal of Saxony were 

 coarsely divided, or bruised, and ignited upon red-hot coals, in- a 

 small glass retort. At the end of this process there appeared, in 

 the receiver, an einpyreumatic water, covered with a thin greasy pel- 

 licle. The loss of weight arising.from this was 51 grains. Pursuing 

 the analysis, Mr. Klaproth was enabled to ascertain that 100 parts 

 of the hydrophanous opal, from Saxony, contain, 



