10 Mographical Account of [Jan, 



latter. This air, as far as Mr. Cavendish's experiments went. Is 

 the same as the inflammable gas from zinc 5 but its specific 

 gravity he found a little higher. 



Mineral waters have at all times attracted the attention of the 

 medical faculty, in consequence of the peculiar properties which 

 they possess, and the medicinal virtues which they are supposed 

 to exhibit. No sooner had the science of chemistry made any 

 progress, than attempts were made by means of it to ascertain to 

 what the peculiar properties of these waters were owing, and 

 to determine the constituents of which they were respectively 

 composed. Some faint; attempts towards the analysis of these 

 waters were made by Boyle. Du Clos attempted to make an 

 experimental analysis of the mineral waters in France; and 

 Hierne published a set of experiments on the mineral waters of 

 Sweden. Though these investigations were rude and inaccurate, 

 they led to the knowledge of several facts respecting mineral 

 waters which chemists were unable to explain. One of these, 

 and not the least puzzling, was the existence of a considerable 

 quantity of calcareous earth in some mineral waters, which was 

 precipitated by boiling the water. Nobody could conceive by 

 what means this insoluble substance {carbonate of lime) was held 

 in solution ; nor why it was thrown down on exposing the water 

 to a boiling heat. It was to determine this point that Mr. 

 Cavendish made his experiments on Rathbone-place water, which 

 were pubHshed in the year 17(>7 (Phil. Trans, vol. Ivii. p. 92) ; 

 and which may be considered as the first analysis of a mineral 

 water, possessed of tolerable accuracy, ever published. All pre- 

 ceding investigations of this kind, when compared with those of 

 Mr. Cavendish, vanish into nothing. Rathbone-place water was 

 at that time raised by a pump, and supplied the streets of London 

 in its neighbourhood with water. Mr. Cavendish found that 

 when boiled it deposited a quantity of earthy matter, consisting 

 chiefly of lime, but containing also a little magnesia. These, 

 he showed, were held in solution by fixed air ; and he proved 

 experimentally that this gas has the property of holding lime and 

 magnesia in •solution, when an excess of it is present. Besides 

 these earthy carbonates, Rathbone-place water contained a little 

 volatile alkali, some sulphate of lime, some common salt, and 

 a little sulphate of magnesia. Mr. Cavendish examined, like- 

 wise, some other pump water of London ; and shbwed that they 

 contained lime held in solution by carbonic acid. 



Dr. Priestley, at a pretty early period of his chemical career, 

 discovered that when nitrous gas is mixed with common air over 

 water, a diminution of bulk takes place; that there is a still 

 greater diminution of bulk when oxygen gas is employed instead 

 of common air ; and that the diminution is proportional to the 

 quantity of oxygen gas present in the gas mixed with the nitrous 



