the Philosophical Character of Dr Priestley. 3 



the general principles of chemistry, and almost without practice 

 in its most common manipulations ; — restricted by a narrow in- 

 come, and at first with little pecuniary assistance from others ; — 

 compelled, too, to devote a large portion of his time to other 

 pressing occupations, he nevertheless surmounted all obstacles ; 

 and in the career of discovery outstripped many who had long 

 been exclusively devoted to science, and were richly provided 

 with all appliances and means for its advancement. 



It is well known that the accident of living near a public 

 brewery at Leeds, first directed the attention of Dr Priestley to 

 pneumatic chemistry, by casually presenting to his observation 

 the appearances attending the extinction of lighted chips of wood 

 in the gas which floats over fermenting liquors. He remarked, 

 that the smoke formed distinct clouds floating on the surface of 

 the atmosphere of the veisel, and that this mixture of air and 

 smoke, when thrown over the sides of the vat, fell to the ground ; 

 from whence he deduced the greater weight of this sort of air 

 than of atmospheric air. He next found that water imbibes the 

 new air, and again abandons it when boiled or frozen. These 

 more obvious properties of fixed air having been ascertained, he 

 extended his inquiries to its other qualities and relations ; and 

 was afterwards led by analogy to the discovery of various other 

 gases, and to the investigation of their characteristic properties. 

 - It would be inconsistent with the scope of this essay to give 

 a full catalogue of Dr Priestley's discoveries, or to enumerate 

 more of them than are necessary to a just estimate of his philo- 

 sophical habits and character. He was the unquestionable au- 

 thor of our first knowledge of oxygen gas, of nitrous oxide, of 

 muriatic, sulphurous^ and fluor acid gases, of ammoniacal gas, 

 and of its condensation into a solid form by the acid gases. Hy- 

 drogen gas was known before his time ; but he greatly extended 

 our acquaintance with its properties. Nitrous gas, barely dis- 

 covered by Dr Hales, was first investigated by Priestley, and ap- 

 plied by him to eudiometry. To the chemical history of the 

 acids derived from nitre, he contributed a vast accession of ori- 

 ginal and most valuable facts. He seems to have been quite 

 aware that those acids are essentially gaseous substances, and 

 that they might be exhibited as such, provided a fluid could 



