amount of the concentrated acid exceeds about 0.5 per cent of the total volume. By employing a considerable excess of ammonium sulphocyanide the precipitation can be made practically complete, at least after a few hours standing, even when the amount of acid is several times the above figure. The use of a decided excess of the sulphocyanide is advisable not only in the presence of acid but also when the solution contains much ammonium salts, on account of the reduction in the solubility of the precipitate thus brought about.* The result of an increase in the ammonium bisulphite in the presence of hydrochloric acid is, except for the liberation of sulphur dioxide, exactly the same as the effect produced by a partial neutralization of the acid by ammonia, namely, the formation of ammonium chloride at the expense of the acid. Unless the amount of acid thus neutralized is quite large, the solubility of the cuprous sulphocyanide in the ammonium salts formed is too small to interfere materially with the completeness of the precipitation. There is, moreover, no objection to the use of ammonia in addition to the bisulphite to neutralize an excess of acid, and where sulphur dioxide is employed in place of ammonium bisulphite, ammonia is in many cases desirable. If, finally, the amount of acid is very large it is unquestionably better to remove the greater part before precipitating the copper. The helpful advice of Prof. F. A. Gooch throughout the course of this investigation is gratefully acknowledged. See the last four determinations of Table II. ART. III.-The Action of Ammonium Chloride upon certain Silicates; by F. W. CLARKE and GEORGE STEIGER. In our previous communications* upon the ammonium. chloride reaction, we have shown that different silicates are very differently affected by the reagent. From analcite, leucite, natrolite and scolecite we obtained new salts, in which the alkali or lime of the original mineral had been replaced by ainmonium. On the other hand, prehnite was practically unattacked, while the pectolite molecule was quite thoroughly broken down, with liberation of much free silica. We now submit the results obtained with several additional silicates; results which serve to emphasize our former conclusions. Our mode of operation has been precisely the same as before. Each mineral, in fine powder, was intimately mixed with four times its weight of dry ammonium chloride, and the mixture was then heated for about five or six hours to 350° in a sealed combustion tube. After cooling, the mixture was leached out with water, and the air-dried insoluble residue was analyzed. Determinations of free silica were effected by boiling the mineral, or its derivative, for fifteen minutes with a solution of sodium carbonate containing 250 grams to the liter. From the solution so obtained the silica was recovered by acidulation with hydrochloric acid and evaporation to dryness. In each case all of the experiments were made upon one uniform sample of material, so that the data for any one species are strictly comparable. So much premised, we may go on to consider the results of our investigations. Stilbite. The specimen selected for study was a nearly white, typical example from Wasson's Bluff, Nova Scotia. The analysis and the fractional water determinations were as follows: * This Journal (4), ix, pp. 117, 345; February and May, 1900. On boiling with sodium carbonate, 1:37 per cent of silica went into solution. After ignition, only 103 per cent was obtained. No silica, therefore, is split off when stilbite is ignited. If the mineral were a hydrous acid metasilicate, H.CaAl,Si,O,, 4H,O, as has been assumed by some authorities, one-third of the silica should have been set free. the metasilicate formula is to be regarded as unsatisfactory. The evidence here presented counts for something against it. 18 Hence Two samples of the ammonium chloride derivative were prepared. In leaching with water the insoluble residue was washed until the washings gave no reaction for chlorine. The chlorine shown in the subjoined analyses is, therefore, present in an insoluble form, and not as adhering ammonium chloride. Dried at 50°, the two products gave the following composition: Sample B was further examined as to the presence of soluble silica, and 1.52 per cent was found. After ignition, only 1.62 per cent went into solution. These results conform to those obtained with the original stilbite, and tend to show that the ammonium derivative is a compound of the same order. In the case of the unignited substance the residue remaining after the removal of soluble silica was thoroughly washed, and then examined for alkali. It was found to contain 9:30 per cent of soda, which shows that the ammonium salt had been transformed back into the corresponding sodium compound. From the foregoing facts it is clear that stilbite, like the zeolites previously studied, is converted by the action of ammonium chloride into an ammonium salt. That is, sodium and calcium are removed as chlorides, ammonium taking their place to form ammonium-stilbite. The reaction, however, is less complete than it was in the cases of analcite and natrolite, but whether this is due to a greater stability of the stilbite molecule, or only to a different degree of fineness in the powder upon which the operations were performed, we cannot say. Neither have we any explanation to offer of the retention of chlorine by the ammonium derivative. Although the amount of chlorine is small, it needs to be accounted for. If we discuss the composition of the stilbite and of its ammonium derivative, the relations between them become. very clear. Neglecting the water as "zeolitic," to use Friedel's phrase, and, therefore, as not a part of the chemical molecule, and also rejecting the 1:37 per cent of soluble silica as probably an impurity, the ratios derived from the analysis give this empirical formula for the mineral: This corresponds to a mixture of ortho- and trisilicates in which Si,O: SiO,:: 286: 43; and uniting these radicles under the indiscriminate symbol X, we have, as a more general expression, 40 or, combining monoxide bases, 140 3321 326 which is essentially RA,X,. Since the SiO, groups are practically equal in number to the sodium atoms, the stilbite is probably a mixture, very nearly, of NaAISIO, and CaAl,(Si,O.), in the ratio of one to seven. This is in accordance with the well-known theory of Fresenius as to the constitution of the phillipsite group, to which stilbite belongs. Stilbite is mainly a hydrous calcium albite, commingled with varying amounts of corresponding orthosilicates of soda and lime." Tak For the ammonium derivative similar relations hold. ing analysis "B" for discussion, rejecting soluble silica and chlorine as impurities, and neglecting all water except that which belongs to the supposable ammonium oxide, the ratios give this formula: Uniting sodium and calcium with ammonium this becomes or, more generally, 3 The derivative, therefore, is a compound of the same order as the original stilbite, with the ratio of 1: 7 still holding between the ortho- and trisilicate groups. This conclusion, however, ignores the presence of chlorine, and is, therefore, inexact to some extent. We are not dealing with ideally pure compounds. Heulandite. Pure, white heulandite from Berufiörd, Iceland, was the material taken for investigation. Upon boiling with sodium carbonate, 173 per cent of sillca went into solution. From previously ignited heulandite only 1.14 per cent was extracted. No silica, therefore, was liberated upon ignition, and a hydrous metasilicate formula for the mineral seems to be improbable. Only one lot of the ammonium chloride derivative was prepared, and its composition, together with that of the heulandite, is given below. Heulandite. Ammonium salt. Here again we have the same kind of transformation as before, but rather less complete than in the case of stilbite. That the ammonium taken up is equivalent to the bases removed, is shown by a study of the ratios. Ignoring water and the soluble silica, the heulandite ratios are as follows: RR", Al,30S923024957 or, uniting bases, R", 48 1301 or very nearly 1:2:2, as in stilbite. Similarly discussed, the ammonium salt gives the ratios In both cases the orthosilicate molecules are few, and the compounds approximate to trisilicates very closely. Chabazite. Characteristic flesh-colored crystals from Wasson's Bluff, Nova Scotia. The analysis and fractional water determinations are as follows: |