Chemical Science. 201 



well known that both M. Despretz * and M. Savart * have pub- 

 lished some account of the peculiar action which takes place 

 when ammonia is passed over heated metals. M. Despretz has 

 more recently read a memoir on the subject, from which we 

 extract the following details. 



The specific gravity of copper has been reduced in the operation 

 from 8.9 to 5.5, without sensible augmentation of weight. In 

 other experiments considerable diminution of specific gravity has 

 frequently been obtained, when the increase in weight has been 

 less than -jj^. Having submitted the same metal to the repeated 

 action of ammonical gas, 100 parts of iron have been increased to 

 111.5 parts by weight. The following are some of several other 

 results. 



9.427 parts of iron became 10.102 or 100 became 107.162 



6.587 7.095 . 100 . . 107.728 



29.960 31.472 . 100 . . 105.046 



7.955 8.553 . 100 . . 107.517 



That the increase of weight thus obtained is not due to oxida- 

 tion from air, water, or carbonic acid, is thus shewn. Air was 

 excluded by passing the ammonical gas for some time before heat 

 was applied, and also after the whole was cold again. Water was 

 excluded by passing the gas through a tube 40 inches long filled 

 with chloride of lime. Carbonic acid gas, by washing the ammo- 

 niacal gas in a solution of potash. The small quantity of water 

 left in the gas by the chloride of lime is considered as unable to 

 cause oxidation, whilst such enormous excess of ammonia as the 

 experiment required is constantly present. The experiment usually 

 lasted 6, 7, or 8 hours. 



If the iron presented the least blueness upon the surface it was 

 returned to the tube and again heated in ammonia. It was only 

 considered good when the iron had the whiteness of unpolished 

 platina. In this state it was brittle and even friable ; light, by 

 comparison with common iron, having frequently a specific gravity 

 of 5. only, and also less changeable in air or water : it was still 

 magnetic and readily soluble in acids. 



M. Despretz thinks that many of the changes in the iron are 

 produced not by a permanent, but by a momentary state of com- 

 bination of one of the elements of the ammonia, and thinks this 

 sufficient to account for the alteration in properties both in it and 

 copper, when the actual weight was^ not increased ^^J^^dth part. 

 To illustrate effects of this kind, he oxidized red-hot iron by the 

 vapour of water, and then reduced it again perfectly by hydrofjen 

 gas ; the cohesion of the iron was very much diminished, and the 

 specific gravity lowered from 7.79 to 6.18. 



The next point was to ascertain whether it was oxygen, or car- 

 bon, or ammonia, or one of its elements, that by a temporary 



* Quarterly Journal of Science, N. S., vol. iii. 476, iv. 205, vi. 175. 



