If there is any difference in a therapeutical point of view, between compounds of the protoxide and compounds of the peroxide of iron, and if any value is to be attached to definite composition in medicines, enabling physicians to administer known quantities to their patients, this state of affairs should not exist. Persons who handle the compounds of protoxide of iron, should be aware of the fact that few substances are more speedily and completely destroyed than these by the action of {230} moist air; thus, one hundred parts of the carbonate of iron, require less than seven parts of oxygen for complete conversion into sesquioxide of iron, and one hundred parts of pure copperas require less than three parts of the same element to effect a like change in all the protoxide of iron which it contains.
As these protoxide of iron compounds, however, oxydate themselves only in the presence of water, the mode of preservation which I would propose, is very simple: It is only necessary to dry them perfectly and to introduce into the vessels in which they are to be preserved, a few small lumps of quicklime, which will keep the air in the interior of the vessel continually dry. To prevent any contamination of the preparation by direct contact with the lime, the latter must be securely folded in one or two thicknesses of filtering paper.
The iodide of iron and the carbonate, phosphate, arseniate, lactate and citrate of protoxide of iron may be preserved in this way, also the anhydrous sulphate (Ferri Sulphas Siccatum), but it is evident that crystallized copperas would not retain a definite composition under these circumstances, because it would soon lose its crystal water. To preserve crystallized copperas, it is best to pulverize the crystals rather finely and dry the powder by repeatedly pressing strongly between folds of filtering paper, before putting up. Some have attempted to preserve the crystals under the surface of strong alcohol, but having tried this plan I must report unfavorably, for although the copperas remained for a while intact, yet, on examination after a considerable lapse of time, a large proportion of sesquioxide of iron was found. In fact, this result was to be anticipated in consideration of the well-known fact that strong alcohol has itself an attraction for oxygen, and always absorbs a certain amount of it when exposed to the air, serving thus merely as a medium for transmitting oxygen to any copperas which may be immersed in it.
I think it may be confidently stated that none of the protoxide compounds of iron should be kept in solution, either in water or alcohol, for medical purposes, unless in vessels {231} hermetically closed. Some say, notwithstanding, that iodide of iron in solution may be preserved by keeping in it a piece of metallic iron, a deposite being formed, however, in the liquid which is supposed to be nothing more than sesquioxide of iron, but in which I strongly suspect the presence of a subiodide of iron, and consequent abstraction of iodine from the solution. Of course, however, this question can only be settled by a chemical examination of the deposit alluded to.
The sulphate of iron is the starting point in preparing all the compounds of iron which are used in medicine, and it is important therefore, to know how to separate easily the impurities which are contingent to this extremely cheap article of commerce. The impurities which commercial copperas most frequently contains are more or less sulphate of sesquioxide, together with a little sesquichloride of iron, and more rarely, traces of the sulphate of copperas, manganese, alumina and lime. A small addition of oxide of silver to the solution will precipitate all chlorine present, and subsequent digestion for a few minutes with carbonate of baryta will remove every trace of sulphate of sesquioxide of iron, and of alumina. Copper may, of course, be removed by immersion of metallic iron. Traces of lime may be separated by recrystallization, but if traces of manganese are present, as is sometimes the case, I, know no way by which it can be separated. I am not aware, however, that the presence of such a trace of manganese in a preparation of iron would impair its therapeutical value. Another method of getting rid of the sulphate of sesquioxide is to acidulate the solution with sulphuric acid and, agitate with some pulverized protosulphide of iron, which will reduce the sesquioxide to protoxide.
When a solution of pure sulphate of protoxide of iron, free from sesquioxide, merely is required for preparing the carbonate or other insoluble protocompound, the method with carbonate of baryta is to be preferred, and in some rare cases when the presence of sulphate of lime in the solution of copperas obtained is of no importance, carbonate of lime may be {232} substituted for carbonate of baryta, and will accomplish the same object.
When a solution of pure protosulphate of iron thus obtained is used for the preparation of carbonate of iron, care must be taken to use for precipitating, a solution of carbonate of soda which is free from silica, phosphoric acid, etc., which if present would surely go down with the precipitate. The precipitated carbonate should be washed with water which has been freed from air by previous boiling and better with water which is still boiling hot, dried as quickly as possible, first by pressure between folds of paper and then in a water bath, and preserved in well closed vessels containing lumps of quicklime as recommended above.
The formulas given in the Pharmacopœias for the preparation of the sesquioxide of iron, which besides being employed as a remedy itself, is used in preparing all the other sesquicompounds of iron used in Pharmacy, appear to be open to great objection on the ground of affording, instead of a pure sesquioxide of iron, an indefinite mixture of sesquioxide with carbonate of the protoxide. No necessity whatever exists for this; the following modus operandi, besides being much less troublesome in its execution than those given by the Pharmacopœias, will furnish a product of constant composition, being an anhydrous sesquioxide of iron free from protoxide, and either chemically pure or very nearly so. The materials required are, five parts of commercial copperas which has been recrystallized once or twice, six parts of crystallized pure carbonate of soda, (Na O, C O2 + 10 HO) or two parts of dry carbonate of soda, and one part of nitrate of soda. (Chili saltpetre). The carbonate and nitrate of soda are dissolved together in one portion of hot water and the copperas in another portion, and the two solutions, after filtrating mixed together, evaporated to dryness and the dry mass exposed to the lowest possible red heat for a few minutes. On pouring water upon the mass thus obtained, sulphate of soda and nitrate of soda dissolve and sesquioxide of iron separates as a heavy powder very easily washed {233} by decantation. When thoroughly washed and dried it appears as a dark reddish brown perfectly impalpable powder, which is perfectly and easily soluble in dilute acids, and even in acetic acid and the composition of which is Fe2 O3.
One great advantage of this process, is an avoidance of the immense tedium of washing the precipitates obtained in the ordinary processes.
I have but one more suggestion to make with regard to preparations of iron, and that is in the preparation of Ferri Pulvis or powder of iron by reduction of the sesquioxide—to propose the substitution of common coal gas as a reducing agent for the hydrogen gas directed by all the formulas, the former being obviously so vastly more convenient and far less expensive.