IRON. 



Acid 



Protoxvd of iron 

 Water ' 



According to Kirwan : 

 Acid 

 Oxyd 

 Water 



It is dccompofcd hy tlio alkalies and alkaline enrtlis ; 

 and by all the falts forming infoluble compounds with ful- 

 phuric acid. 



Oxy-fulphat of /roB.— This fait confifts of the fulphiiric 

 acid united to the pcroxyd of iron. Its folution in water is 

 cf a deep reddifh-brown colour. It is infufceptible of cryf- 

 tallization. Hence, the green cryftals feparated in making 

 copperas are perfectly di linft in their nature from the fait 

 which is left in the remaining liquid. When the fiilphat 

 is expofed in a ftate of folution for a length of time, it 

 affumes a red colour, and is converted into this fait ; fo that 

 we never find the common fulphat in mineral waters, but the 

 oxy-fulphat. This change may be more fpeedily brought 

 about by heating it wi^h nitric acid. A quantity of nitrous 

 gas is evolved, and, according to Mr. Davy, ammonia alio ; 

 the former from the decompofitiou of the acid, the latter 

 from the decompofitiou of both the acid and the water. 

 The fluid gradually afl'iimes a deep brown colour. It has a 

 ftrong aftri'ogent talte, much rtfembling the juice of floes. 

 When this '.llis formed without the addition of water, it is 

 exceedingly heavy, and concentrated, and of a deep brown 

 tint, approaching to blacknefs. If concentrated fulpluiric 

 acid be poured mto it fuddenly, it lofes its brown colour, 

 and becomes of a clear white, having the confiftence of thick 

 cream. It is fo foluble in water, that when evaporated 

 flowly, inrtead of cryftallizing, it affunies the form of fyrup. 

 If too much heat be applied, however, the oxyd either pre- 

 cipitates, or it affumes the form of a fub-falt, and becomes 

 infoluble. 



Since the oxy-fulphat differs from the fulphat in the pro- 

 portion of oxygen only, feveral fubftances reconvert it into 

 that fait, by abftraiSing the excefs of oxygen. If it be 

 kept, for inllance, for fome time in a clofe-llopped bottle 

 with iron-filings, the metal becomes oxydized, and the 

 whole is ch.iiiged to the fim.ple fulphat. 



Gay-LuCfac has lately fhewn that the quantity of acid in 

 any metallic fait is in proportion to the quantity of oxygen 

 in the metal. (Memoires d'Arcueil, t. ii p. IJO-) Hence 

 no additional acid is required in converting this fait into the 

 fulphat. 



Tin, and feveral other metals, produce the fame effeft. 

 The excefs of oxygen may iiillantly be taken away by paff- 

 irgfulphurettedhydrogengas through the oxy-fulphat. This 

 gas reduces the oxyd exaftly to a minimum of oxydation, to 

 the ftate of pvotoxyd ; and hence the reafon why this gas 

 does not precipitate iron from its folutions. 



The oxy-fulphat may becafily feparated from the fulphat ; 

 the former being foluble in alcohol, which the latter is not. 



From the method required lo form this oxy-falt, it will 

 appear that there are feveral fnbllances which may be em- 

 ployed to give their oxygen to the fulphat of iron. Of tliefe 

 are the nitric ar.d oxy-muriatic acids. And by pouring a 

 2 



folution of gold in^o a folution of this fulphat, the oxy- 

 fulphat is produced, and the gold becomes metallic. 



Dr. Thomfon enumerates feveral triple falts, formed by 

 the fnlphuric acid with iron and other metals. 



1. Sulphat of iron and copper. 



2. Sulphat of iron and zinc. 



3. Sulphat of iron and nickel. 



The former of thefe fometimes exifts in the blue vitriol of 

 commerce, which is a very great evil to colour-makers. 

 The iron precipitates with the copper, and deftroys the 

 beauty of the latter. In order to afccriain whether iron be 

 prei'ent in blue vitriol, difTolve a fmall quantity in a wine-glals, 

 and add aqua ammonia till it fmells ftrong of the latter. 

 The oxyd of copper will be diffolved, and the oxyd of iron 

 left at the bottom. By ftai:ding for fome time, the pre- 

 cipitate becomes yellow and very confpicuou-i. It is even 

 faid that fome of thefe falts have triple bafes. The two 

 hitherto obferved are as follows ; 



1. Sulphat of iron, zinc, and nickel. 



2. Sulphat of iron, copper, and nickel. 



Sulphite 0/" /»•&«. — Berlhollet has given us an account of a 

 compound of iron with the fulphurous acid. When iron is 

 expofed to the adlion of this acid, it becomes fpeedily oxy- 

 dized ; but what is fingular, not at the expence of the 

 waterras is the cafe with the fulphuric acid ; but it appears- 

 that the acid is decompofed, the oxygen luiiting wi;h the 

 iron, while the fulphur combines with the fait. Hence 

 this fulpliat of iron is always contaminated with fulphur. 

 The fulphurous acid has a'lefs afHnity for iron than the 

 fulphuric ; and if the latter be added to the fulpliat, its acid. 

 is difengaged in the form of gas. 



Kitrat of Iron. — The nitric acid has very violent aftion 

 upon iron, and an abundance of the red fumes of nitric 

 oxyd are difengaged. The fame thing in fome meafure 

 takes place with this acid, as has been remarked with regard 

 to the fulphuric. If it be more than a certain flrength the 

 ailion is feeble, until a certain portion of water is added. 

 The fame explanation will anfwer in both inftances. The 

 nitric acid does not diffolve the nitrat at firft formed, the 

 prelence of which interrupts the future progrefs of the 

 operation. When the folution is made with much water 

 the iron is oxydized to a minimum, and the fait formed is 

 the proper nitrat. It is of a pale green colour. The vefTel 

 in which this folution is made fliould be kept in water as 

 cold as pofTible, elfe it will abforb too much oxygen, and 

 pafs to the oxy-nitrat. 



Oxy-nitra! of Iron. — When iron is afted upon by the kfs 

 diluted acid, and with heat, the fait formed is the oxy-nitrat. 

 The folution is of a deep brown, refembling the oxy-fulphat. 

 It has a flrong aftringent taftc, and turns vegetable blues 

 red. When the folution is boiled the oxyd is partially pre- 

 cipitated ; nor will it afterwards diffolve in the nitric acid. 

 This has furnifhed one means of feparating iron from other 

 fubftances in the analyfis of minerals. 



We are indebted to Vauquelin for a method of obtaining 

 this fait in a cryftalhzed ftate. The method he recommends, 



to keep the black oxyd of iron and ftrong nitric acid 



together for a length of time, till the cryftals appear. Ti 

 have an acid tafte, and are d "' ' 

 is that of a four-fidtd prifm. 



deliquefcent. The 



upcar. 1 11 

 form of th. 



The alkalis precipitate the oxyd of iron from this fa!* of 

 a fine yellow colour, and yield a produft which is valuable 

 to painters. 



Muriat of Iron. — The muriatic acid, like the fulphuric 

 and nitric, ails feebly tipon iron, except jt be diluted to a 

 certain extent with water. It differs from the latter, and 



agrees 



