106 PHILOSOPHICAL TRANSACTIONS. [aNNO I765. 



the basis of sea-salts: the same which is procured from the Spanish barilla, and 

 from our own kelp. 



The mineral alkali differs from the vegetable in its ready crystallizing without 

 any addition of fixed air, which is necessary to make the latter take the form of 

 crystals;* and in its not melting in a moist air; and on this last account it is a 

 much more commodious ingredient in medicinal powders, than the vegetable 

 alkali, as it is not like this apt to run per deliquium; but on the contrary, instead 

 of attracting moisture from the air, it is robbed by the air of its own moisture, 

 so that its crystals soon lose their transparence, and are turned to powder. The 

 natron liquifies in a very gentle heat: it resembles the vegetable alkali in taste 

 and fixedness, and like that is used in making soap and glass: and they are both 

 applicable to most of the same purposes. Of the crystals of natron, when very 

 dry, but yet with scarcely any white powder on them, 100 gr. may be dissolved 

 in 384 gr. of water, when Fahrenheit's thermometer is at 37. Such crystals 

 quite dry, and just inclining to grow white, will lose -r°^Vo of their weight if 

 dried, with a heat sufficient to scorch paper. 



" The vegetable alkali has a stronger affinity to the acid spirits of vitriol, nitre, 

 and marine salt, than the fossil;" for I, if the common alkali be added to a satu- 

 rated solution of Glauber's salt in water, the spirit of vitriol will leave the natron, 

 and, uniting itself with the vegetable fixed salt, will form vitriolated tartar; 

 which being of difficult solution, much of it will crystallize and fall to the bottom; 

 while the natron, robbed of the vitriolic acid, remains dissolved together with a 

 small portion of the vitriolated tartar. 2. Gr. l66 of quadrangular nitre were 

 dissolved by heat, in a solution containing gr. 138 of pearl-ashes. On cooling 

 there shot some crystals of common nitre, the nitrous acid having left the fossil 

 alkali, which is the base of quadrangular nitre, to join itself with the pearl-ashes. 

 3. Gr. 500 of sal-gem, which seemed quite free from sal catharticus amarus, 

 were dissolved by heat in a solution of gr. 654 of pearl-ashes. There shot a 

 considerable quantity of sal sylvii mixed with fossil alkali, which had been ex- 

 pelled by the pearl-ashes from the marine acid. These experiments were made 

 and communicated to Dr. W. H. by the Hon. Henry Cavendish, 



Besides the properties which have been mentioned, the natives of the Canary 

 islands have found out, that they can make matches by dipping paper or tow in 

 a strong solution of natron, which will then burn, except that they do not sparkle, 

 almost as well as if they had been dipped in a solution of nitre, though on trial 

 no nitre appears to be mixed with it. The salt of barilla and kelp he finds by 

 experience, to have this property, but in a less degree, which may be owing to 

 their not being perfectly free from other salts. 



• See Dr. Black's experiments in the Edinburgh Essays, vol. 2, p. 218. — Orig. 



