Page images

crucible capable of holding three times the bulk of mixed powder. The platinum crucible should then be placed in one of earthenware, with a little magnesia on the bottom. (I always prefer the crucible made in France, called Beaufay's crucible, to inclose platinum crucibles when heated in a furnace, as their form and cleanliness make them superior to the Hessian crucible for this purpose.) The crucible may then be covered and introduced in any form of furnace where a bright red heat can be procured.

17. I have been using a common open portable furnace, heaping charcoal over the top of the crucible; and so easily does the effect take place that in no instance has there been a failure of complete decomposition with as simple a means of heating as the above; and I have ascertained that an alcoholic lamp with a large circular wick, such as Jackson's lamp, urged with a bellows, will answer for making a complete decomposition of zircon in twenty-five minutes. This circumstance is not stated to recommend the use of a lamp for every mineral decomposition when a simple portable furnace and charcoal are so accessible, and their effects so much more to be depended upon than a lamp. From thirty minutes to one hour's exposure to the heat is recommended.

18. It was an important point to test first how far this mixture could decompose the silicates without distinction as to their containing alkalies; for it was a very simple conclusion that if those silicates most difficult of decomposition, and containing no alkalies, were completely decomposed by this process, all others must naturally give way under its action. The silicates experimented on were zircon, kyanite, beryl, topaz, spodumene, margarite, margarodite, and feldspars of different descriptions. All were readily decomposed by the method just hydrochloric acid (the common acid may be used), adding an excess of the carbonate; lime-water or milk of lime is then poured on the solution until it is alkaline. By this means any oxide of iron, alumina, or magnesia will be thrown down. To the hot filtered solution a solution of carbonate of ammonia is added, and the precipitate washed several times with distilled water. It is best to prepare one's own carbonate of lime, for as a general rule little reliance can be placed on the carbonates of lime, baryta, strontia, etc., sold as being precipitated by carbonate of ammonia, for in more than one instance I have found the carbonate of baryta, sold as a carbonate of ammonia precipitate, to contain soda.

described, and without any particular care in levigating them. One gramme of the zircon, for instance, after being crushed in the diamond mortar, was rubbed up for fifteen minutes in a large agate mortar, and used. Its complete decomposition was not only shown by its solution in hydrochloric acid, but by the amount of zirconia obtained, which was 64.8 per cent., with little iron. This concludes the first point to be considered in this article-namely, the means necessary to render the silicates soluble. The next point is the separation of the alkalies.


19. The platinum crucible, with its fused contents, is laid on its side in a capsule of platinum or porcelain. The latter can be used with perfect safety to the accuracy of the result. A quantity of dilute hydrochloric acid is poured into the capsule, one part of acid to two of water. The whole is heated over a lamp, when the contents of the crucible are rapidly dissolved out; the crucible is taken out and washed over the capsule; the contents of the capsule are then evaporated to dryness over a sand-bath; and, if thought necessary, it may be completed over the lamp without danger of the spitting which occurs in the soda fusion. This evaporation to dryness is not absolutely necessary; but the advantage of it is that any great excess of hydrochloric acid is got rid of, and the precipitate in the next operation is less bulky than it otherwise would be.

20. To the dry mass a little hydrochloric acid is added, and then three or four ounces of water, or more, as the occasion may require It is then boiled for a short time in the same capsule, allowed to cool down a little, and then a concentrated solution of carbonate of ammonia is slowly added until there' is an excess of the same. The solution becomes at first quite thick with the precipitate, but in a short time (especially with a little warming over the lamp) the precipitate accumulates in a more or less granular state, and afterward occupies less space in the filter than the alumina it might contain (in a feldspar, for instance) were this latter precipitated separately by ammonia; and this circumstance is of much importance in diminishing the length of the operations and the amount of water accumulated by filtering it from several precipitates.

21. It will be seen that thus far the operations have been carried on in the capsule in which the fusion was dissolved. The contents of the capsule are now thrown on a filter; but before doing this it is well to pour on a little of the solution of the carbonate of ammonia, and see if the clear part of the liquid be rendered turbid; in other words, ascertain if sufficient carbonate of ammonia had been originally added.

22. The solution that passes through the filter contains much sal ammoniac, the alkalies of the mineral, and a little lime. If magnesia be one of the ingredients of the silicate examined, some of this is also present; and in still rarer instances some of the earths soluble in carbonate of ammonia. This latter complicates in no degree the remaining steps in the analysis. It is best to let the filtrate pass into a glass flask. The washings of the filter are collected in another vessel and concentrated to a small bulk, added to the first filtrate, and the whole boiled for some time to drive off the carbonate of ammonia.* When no great haste is required in the matter the whole filtrate (first portions as well as the washings) are collected in a beaker and concentrated over a sand-bath. What remains now to do is to separate from the alkalies the substances above alluded to. I commence by getting rid of the sal ammoniac, and this brings me to the third part of this paper.


23. This is probably one of the greatest annoyances to the analyst in his examination of minerals: first, from the manner in which the salt creeps up the sides of the vessel in which the evaporation to dryness is carried on; and secondly, from the great difficulty of preventing loss of the chlorides of the fixed alkalies during the volatilization of the sal ammoniac. A better idea is formed of this by an experiment with a known quantity of the alkalies mixed with sal ammoniac. An array of the precautions requisite to be taken can be seen in Rose's last edition (German), pages 6 and 7. Owing to these difficulties, which my experience has often led me to contend with,

*What remains in the filter is silica, alumina, fluoride of calcium, oxide of iron, carbonate of lime, etc.

the method about to be mentioned was contrived. It recommends itself both on account of its simplicity and certainty of operation.

24. Having some time back noticed the decomposing effect produced by heating sal ammoniac with nitric acid, the nature of the decomposition was investigated to see how far it could be made use of to decompose entirely the sal ammoniac. The result of the investigation was that the sal ammoniac could be completely decomposed at a low temperature into gaseous products, and it was immediately adopted in my analytical process with the greatest satisfaction, both as to accuracy of results as well as economy of labor.*

*Formation of almost pure Protoxide of Nitrogen by the action of Nitric Acid on Sal Ammoniac.—The experiments made with the nitric acid heated with sal ammoniac to test the character of the decomposition have resulted in the discovery of a new method for procuring protoxide of nitrogen with the aid of a very low temperature. Among the experiments the following were quantitative. Two grammes of sal ammoniac were placed in a glass flask, and half an ounce of nitric acid poured upon it; the flask was connected with a small wash-bottle containing a little water, and from this latter a tube passed into a pneumatic trough filled with hot water; heat was applied to the flask, and before the temperature reached 140° Fah. a gas began to be given off, and at 160° it came off rapidly, and continued to do so after the lamp was withdrawn. A small amount of red fumes appeared in the flask that were condensed in the wash-bottle. The gas that passed over was collected in a receiver, and measured one thousand and eight cubic centimetres. The gas smelt of chlorine. The flame of a candle burnt with an increased brilliancy when introduced in it. The candle was reignited when extinguished if a burning coal remained on the end of the wick. No red fumes were formed when it came in contact with the air, and the gas was absorbable by cold water. The properties were those of protoxide of nitrogen. In another experiment the gases were collected at different stages of the process, in vials over hot distilled water, and a solution of caustic potash introduced and shaken up for some time. This latter was subsequently analyzed for the chlorine it absorbed, and in three different portions, collected at the beginning, middle, and end of the process; the proportions of the chlorine to the whole bulk of the gas were one fifty-seventh, one twentyninth, and one sixteenth. The amount of protoxide of nitrogen due to the ammonia in two grammes of sal ammoniac and its equivalent of nitric acid is eight hundred and eighty-seven cubic centimetres. The gas freed from chlorine, on being shaken up with cold water for some time, was found to be almost entirely absorbed by the water. What remained was a mixture of nitrogen and a little air. Some nitrous or hyponitrous acid forms during

25. The manner of proceeding is as follows: to the filtrate and washings concentrated in the way mentioned (22), and still remaining in the flask, pure nitric acid is added-about three grammes of it to every gramme of sal ammoniac supposed to exist in the liquid. A little habit will suffice to guide one in adding the nitric acid, as even a large excess has no effect on the accuracy of the analysis.

26. The flask is now warmed very gently, and before it reaches the boiling-point of water a gaseous decomposition will take place with great rapidity. This is caused by the decomposition of the sal ammoniac in the manner described in the note. It is no advantage to push the decomposition with too great rapidity. A moderately warm place on the sand-bath is best adapted for this purpose. With proper precautions the heat can be continued and the contents of the flask evaporated to dryness in that vessel; but it is more judicious to pour the contents of the flask, after the liquid has been reduced to half an ounce, into a porcelain capsule (always

the whole process if concentrated nitric be used. If, however, it be diluted. little or none is formed, and the gas is readily given off at about 212° Fah.

In all my experiments the protoxide of nitrogen constituted from seven eighths to twenty-four twenty-fifths of the gaseous products, and when washed from its chlorine by a little lime-water or soda possessed all the properties of pure protoxide of nitrogen; and I would recommend it as a convenient way of forming this gas, especially when not required for respiration.

The character of the decomposition which takes place is somewhat curious and unexpected. At first I supposed that the decomposition resulted in the formation of equal volumes of NO, Cl, and N; but it appears that such is not the case, and that all but a very small portion of the ammonia, with its equivalent of nitric acid, is converted into NO, the liberated hydrochloric acid mixing with the excess of nitric acid. A little of the sal ammoniac and nitric acid does undergo the decomposition first supposed, and in this way only can the small amounts of chlorine and nitrogen be accounted for. At the time this method was first tried I also tried the decomposing effects of nitrate of ammonia on sal ammoniac, that has been shown by Mauméné (Comptes Rendus, October 15, 1851) to result in the formation of chlorine and nitrogen; but the difficulty of controlling the decomposition once commenced, the puffing-up of the mixture, and the necessity of having the salts dry to begin with, render this method (which was proposed by the author for forming chlorine) useless in processes for removing the sal ammoniac in analysis.

« PreviousContinue »