~ 
J. M. Ordway on Nitrates of Iron. 321 
In speculations respecting the cause of passivity, it has 
not unfrequently been taken y for granted that this singular 
preparato con il commune metodo AzO, +2HO,, cessa di esserlo 
posto a contatto con l’acido azotico fumante AzO,+ O, cioéa 
dire con questo acido privato de un equivalente di acqua,” 
brightens and undergoes no further change. Initial tempera- 
will go on to the end, while a thorough and constant stirring 
ae would so distribute the small amount of heat evolved on first 
in. The action continued till the metal was all gone. 
Tn another experiment with the acid at 33° C., the action quickly 
* 26. Nigus acid of sp. gr. 1°38 warmed to 31° C., soon rendered iron 
wire passive. pee 
Some of the same acid at 32° C., kept on acting till the iron was used up. 
_ 17, a—A nearly pure and colorless acid of sp. gr. 1-39 warmed to 30 
but when such acid was heated to 31° C., 
before adding the iron, the action kept on. wag 
(sonia cetaa Yon wil of sp. gr. 189 warmed to 41°5°C. exercised 
