upon Bismuth and other Metals. 309 



bismuth will be found in the peculiar state. This latter effect 

 will be more frequently obtained by agitating the liquid, so 

 as to bring a fresh surface of acid into contact with the bis- 

 muth. But the peculiar state is never produced in this way 

 till the original surface of the bismuth has been dissolved 

 away, and a fresh surface exposed to the acid. It is easy, 

 however, to procure a surface of bismuth, which will always 

 be inactive, even when first introduced into acid of the above 

 strength, not only at the temperature of 50° Fahr., but even 

 at that of 80°, at which degree unattached fragments of bis- 

 muth always dissolve with great rapidity. For this purpose 

 all that is necessary is to fill a glass tube about yV^^ ^^ ^^ 

 inch in diameter with fused bismuth, and then to file it across, 

 so as to expose a circular section of bismuth to the acid. The 

 surface thus obtained was always found to be in the peculiar 

 state on its first immersion in the acid. The greatest care 

 was taken to render the surfaces of the unattached fragments 

 perfectly similar by filing, and to bring all to the same tem- 

 perature. 



Are we to suppose that in this case the glass acts the part 

 of an electro-negative metal, and induces the peculiar state 

 by developing an electrical current? This supposition ap- 

 pears extremely improbable, and some experiments which 

 I made in reference to this view were unfavourable to it. 

 The influence of the glass is most probably mechanical, as 

 the plane surface of the bismuth alone exposed to the acid 

 opposes its solution, and thus develops the peculiar state. It 

 must be acknowledged, at the same time, that there is some 

 difficulty in supposing that so slight a mechanical difference 

 should have the effect of arresting a powerful chemical ac- 

 tion. 



The phaenomena presented by the other metals agree in their 

 general features with those already described, although they 

 differ slightly in some of the details. 



The peculiar state of tin closely resembles that of iron. 

 Nitric acid of sp. gr. 1*5 exerts no action whatever upon tin; 

 at least I have preserved that metal in acid of this strength 

 for several weeks, and its surface still remains untarnished *. 

 If a pencil of tin is dipped into nitric acid, sp. gr. 1'47, at 

 50° Fahr., it is immediately attacked and its surface becomes 

 densely coated with peroxide ; but if the acid is placed in a 

 platina vessel, with which the tin has been connected before 

 immersion, the acid will no longer act upon it, and on breaking 



* In Dumas's Traite (vol. i.) it is stated that nitric acid of sp. gr. 1*5 

 acts violently upon tin, which is insoluble in acid of sp. gr. r48. This is 

 certainly a mistake, piovided pure nitric acid is employed. 



