2Q0 PHILOSOPHICAL TRANSACTIONS. [aNNO 1782. 



fire, continued white, powdery, and unaltered. Thirty grains of this earth 

 were mixed with an equal weight of dry fossil alkali, and the same quantity of a 

 fine white quartzy sand was mixed with the same proportion of the same alkali : 

 the two mixtures were put into 2 small crucibles, which were surrounded with 

 sand in a larger one, that both might be exposed to an equal heat. They both 

 began to melt at the same time; and at about 80° of the thermometer they 

 had formed perfect transparent glasses. Though these properties may not, per- 

 haps, be thought sufficient of themselves, for determining with certainty that 

 this substance is of the siliceous kind, yet, when joined to the negative proofs, 

 of its not belonging to any other known order of earthy bodies, they afford the 

 fullest evidence which the nature of the subject can admit of, that the indis- 

 soluble part of this clay is truly siliceous; and consequently that the clay consists 

 of 2 parts of pure siliceous earth, to 3 parts of pure argillaceous or aluminous 

 earth. 



XX. An Analysis of Two Mineral Substances, viz. the Roivley-rag-stane, and 

 the Toad-stone. By William Withering* M. D. p. 327. 

 In a prefatory letter to Dr. Priestley, Dr. W. states that he had sent the 

 results of his examination of the toad-stone and the Rowley-rag-stone ; being 

 part of a plan which he had long before formed for a chemical analysis of all the 

 substances that are known to exist in the earth in large quantity. Some years 

 before he transmitted to the r. s. an analysis of the different marles found in 

 Staffordshire ; and in the course of experiments which this subject had led him 

 to, he found it convenient to form some new tables, and to enlarge some that 



* Dr. Withering practised physic, for a great number of years, with much celebrity, at Birmingham ; 

 near which place he died in 17!iy, in the 58th year of his age. He was initiated in the medical 

 profession under his father, who was an apothecary at Wellington, in Shropshire, and was after- 

 wards sent to Edinburgh, where he took his degree of m. r>. in 1766. In 17 70 he published his 

 Arrangement of Plants growing naturally in Great- Britain, in 2 vols., and which has since gone 

 through 4 editions, with numerous improvements and additions, so as to make + vols, in 8vo. It is a 

 most complete national Flora. In 177*) appeared his Account of the Scarlet Fever and Sore Throat, 

 and in 1785 his Account of the Foxglove. In both these publications he appeared to great advan- 

 tage as a practical physician. And although he was not the first to point out the diuretic powers of 

 the foxglove in hydropic affections (that having been done before by Dr. Darwin) yet he produced a 

 great number of cases in which it had been given with success, together with many useful admoni- 

 tions concerning its preparations and doses. In 1783 he published a translation of Bergmann's 

 Sciagraphia Regni Mineralis, under the title of Outlines of Mineralogy ; before which time he had 

 shown that he had bestowed considerable attention on chemical pursuits, by some papers inserted in 

 the Philos. Trans. It should be added that, while he was at Lisbon for the benefit of his health in 

 17 05, he analyzed the hot mineral waters in the neighbourhood of that city. For other particulars 

 concerning the life of this ingenious physician and naturalist, the reader is referred to the Gent. Mag. 

 for l7y;;, a "d t0 l^ r - Duncan's Annals of Medicine for die same year. 



