occasionally remain behind, we preferred the additional fusion to get at that small quantity, and to entitle it to rank as a method by which all but the merest trace of the alkalies could be extracted from the insoluble silicates.

59. The proportion of sal ammoniac added to the carbonate of lime as here recommended is arrived at after numerous experiments. By increasing the sal ammoniac, and thereby augmenting the amount of chloride of calcium formed, the mass fuses more thoroughly, but the water does not disintegrate it as completely as when the ammoniacal salt is less; also the accumulation of this latter at the end of the process is less, an object not to be disregarded. The advantage of thus estimating the alkalies in insoluble silicates is obvious. The long routine of separating silica, alumina, lime, etc., is done away with; the accumulation of chloride of ammonium is very trifling; and lastly, the alkalies are obtained directly in the form of chlorides. The method will vie in accuracy with any other, including the one already mentioned in the first part of this paper; and at the same time it is unequaled in simplicity, speed of execution, and constancy of results.

60. In examining for alkalies qualitatively, one fusion will of course be all that is necessary, and the action of the water need not be continued more than thirty minutes before filtering. This method answers even when boracic acid is present in the silicate. The manner of proceeding in such a case will be mentioned in a future paper on the determination of boracic acid in minerals.

61. There is nothing new in the attempt to dissolve out the alkalies by water from a silicate that had been heated with lime. M. Fuchs used the method for procuring lithia from lepidolite; but of course his efforts were entirely directed to procuring the lithia from the mineral, and not to estimating its quantity, as the method he followed could not have furnished such results. I have also lately learned that Mr. A. A. Hayes, of Boston, proposed and employed a mixture of chloride of calcium and caustic lime to decompose alkaline silicates, heating over a lamp, and subsequently treating the mass with water to extract the alkalies or chlorides. As little has been heard of this process, I presume the author found it defective. If we are correctly informed, the proportions used were three

parts of chloride of calcium and one of caustic lime. Experience proves that, however readily such a mixture may reduce the feldspars, it fails when tried on kyanite, zircon, micas, and other silicates difficult of decomposition. This arises from the fact that the chloride of calcium has but little decomposing effect on the silicates, its action being simply that of a menstruum in which the lime can act conveniently on the mineral.

62. The use of lime or its carbonate mixed with chloride of calcium or chloride of ammonium, for the purpose of effecting the decompositions alluded to, would be considered by me of questionable utility if the mixture were not so proportioned and employed as to decompose the most difficult silicates, if necessary; for unless this be done we can at no time be certain that the decomposition is complete. As a general rule for decomposing silicates by lime or soda, it is far better to use a charcoal fire than the flame of a lamp, as it is better to heat too high than not to heat sufficiently the mineral to be acted on.

COMPLETE ANALYSIS OF AN INSOLUBLE SILICATE ON ONE PORTION OF THE MINERAL.

63. The effort to accomplish an analysis of this description deserves no encouragement, from the almost invariable inaccuracy attending the results. If we have a given quantity of any one of the silicates alluded to requiring analysis, we had better subdivide it, however small the entire quantity may be, ascertain one set of ingredients by the soda and the other by the lime fusion; for the results thus obtained may be relied on as more accurate than those furnished by an analysis of the whole quantity through the agency of baryta or hydrofluoric acid.

64. Should it be desired to undertake the analysis on a single portion, I would recommend the silicate to be attacked with carbonate of baryta mixed with the chloride-three to four parts of carbonate and two of chloride. This mixture can be made to decompose all silicates at a much lower temperature than when the carbonate alone is used, but its action is not near so powerful as the carbonate of lime and sal ammoniac.

65. This terminates an account of my labors in the determination of the alkalies in insoluble silicates. The conclusions

have been arrived at from more than two years' experience and over a hundred alkali determinations by myself and others made on minerals of the most varied composition. In my laboratory an accurate alkali determination is one of the most simple and speedy analytical processes now conducted, and the presence of magnesia in no degree complicates the result. A little experience will no doubt bring others to the same conclusions. Many singular decompositions of salts have been noticed in the course of these researches; but as they do not bear directly on the object of this article they will be made known on another occasion.

Many analytical processes mentioned in this article can be applied when operating on soluble silicates.

CONVERSION OF THE SULPHATES OF THE

ALKALIES

INTO THE CARBONATES, TARTRATES, &c., IN THE
MOIST WAY.

Having had occasion more than once to convert small quantities of the sulphates of the alkalies into carbonates, I have for several years employed a process that has been found both certain and convenient; in some recent investigations it has been used, and as it has never been described it may not be unimportant to explain the nature of the process and its results. The agent used to produce the conversion is carbonate of baryta, made by precipitation; where precise results are required the carbonate should be prepared by carbonate of ammonia. The manner of producing the decomposition is as follows: Dissolve the sulphate of potash in water, using about twenty or thirty grammes of water to every gramme of the sulphate, and saturate the solution with carbonic acid by passing a current of carbonic acid into it; or, what is better, dissolve in the beginning the sulphate in water already saturated with carbonic acid; now add to this solution precipitated carbonate of baryta, in the proportion of about one and a half of the carbonate to one part of the sulphate. It is always best in adding the carbonate to rub it up in a mortar with a little water, so as to form a thick cream, for by so doing it mixes well in the solution.

This operation is performed in a bottle that can be well corked with a cork or gum stopper; now agitate the bottle frequently, or, what is still better, attach it to a piece of machinery that will agitate the bottle. Many laboratories have such, and it is a very useful one in many experiments. In a longer or shorter space of time the decomposition will be completed; pour the solution into a capsule and heat to the

CONVERSION OF THE SULPHATES OF THE ALKALIES. 223

boiling-point; the solution will then contain only carbonate of potash.

The reaction is readily understood; the carbonic acid in the water dissolves a little carbonate of baryta, which is immediately precipitated in the form of sulphate, carrying down a portion of the sulphuric acid of the soluble sulphate, and replacing the same with carbonic acid; this is rapidly repeated through the agency of the free carbonic acid, until the decomposition of the sulphate is complete.

Among many experimental results I will give the following: Five grammes of the sulphate of potash dissolved in carbonicacid water, to which was added seven grammes of precipitated carbonate of baryta, after four and a half hours' shaking (being attached to a suitable piece of machinery), on testing showed not a trace of sulphuric acid, care being taken to wipe the neck of the bottle near the end of the stopper before pouring out the liquid.

Other experiments, varying in proportion, gave similar results. I tried to substitute the natural for the precipitated carbonate of baryta, but with very unsatisfactory results.

DIRECTIONS FOR CONVERSION OF THE ALKALINE SULPHATES INTO TARTRATES, OXALATES, ETC.

As the tartrate and oxalates of baryta are but very slightly soluble in water, we can not form the alkaline salts of these acids by direct double decomposition of the sulphates of the alkalies and the tartrate, etc., of baryta, as in forming the alkaline chlorides from the sulphates; but it is easily done by the following indirect process.

Add to the alkaline sulphates in solution, in a porcelain capsule, carbonate of baryta rubbed up into a thick cream in the proportion of about five of the sulphate to seven of the carbonate of baryta; heat the mass and add little by little the requisite quantity of tartaric or oxalic acid; solution of the baryta and precipitation of the sulphuric acid take place rapidly, and the decomposition is soon completed.

I have used this process in forming the bitartrates in the process of separating potassium, rubidium, and cæsium, that were in the form of sulphates.