Page images

too often by paying attention to the strength of the reaction of the fluid upon the litmus-paper.

In most marls which have served as the subjects of my experiments more or less alumina is to be found, a part of which is dissolved by the acid, of which part a very good use can be made. While adding the ammonia the alumina immediately around where the ammonia falls is thrown out of solution; and if we stir the liquid, the alumina will be redissolved so long as there is any free acid; so that when the flocks of alumina are no longer taken up we are furnished with an assurance that the process is nearly completed. The acid that the alumina and iron take up is acted upon by the ammonia with almost the same readiness as if free, so that no cause of error is to be apprehended from that source.

It may sometimes happen from oversight that too much. ammonia is added. Notwithstanding this the analysis need not be lost. Still holding the instrument in the left hand over the cup, having of course arrested the flow of the fluid, we pour some of the acid solution into a wine-glass, introduce the small end of the acid instrument into it, and allow it to rise on the inside to either of the small marks, and add this acid to the liquid, and go on as before with the experiment, and at the conclusion read off what is indicated, and to it add 10 or 20 according as we may have added the acid measured by the first or second mark.

After what has been said a few words will suffice to explain how the instrument operates.

It takes 50° of acid to dissolve fifty grains of carbonate of lime, or 1° to dissolve one grain; and it takes 2° of the ammonia solution to neutralize one of the acid; and therefore in treating a substance consisting in part of carbonate of lime, for every grain that is present one degree of the acid is taken up, so that when we come to add the ammonia we know how much of the acid is taken up by the quantity of ammonia left behind, thereby knowing the number of grains of carbonate of lime, which we multiply by two (as fifty grains of the substance was used) to arrive at the percentage. This multiplication is not actually performed, as the instrument is so graduated as to dispense with it.

Were it at all necessary to give any evidence of its easy

application, I might state that it, along with the fluid, has been placed in the hands of persons entirely unacquainted with chemistry, and even with the principle of the instrument, and they have, with some little instruction in the manipulations necessary, obtained results only one or two per cent. out of the way in their first examination. The instrument is designed specially for examining calcareous manures.



This note is intended as an appendix to my researches for determining the alkalies in insoluble silicates.

During that investigation many novel and interesting reactions were observed, several of which have already been alluded to. I present here one or two others of some interest.

It is well known that if nitric acid be added to a chloride, or hydrochloric acid to a nitrate, more or less of a decomposition will in either case ensue; but I believe it is not generally known how ready and complete the replacement is when nitric acid is heated with chloride of potassium or of sodium.

Among the experiments made, forty grammes of nitric acid were boiled gently with six grammes of chloride of potassium, and in twenty minutes no trace of chlorine could be found in the liquid. The same is true when the chloride of sodium is used. The operations appear to depend on the oxidizing property of the nitric acid, with the liberation of chlorine that combines with some of the elements of nitric acid to form the chloronitric acid that readily passes off. The decomposition of the nitrates of the alkalies by hydrochloric acid does not readily take place, it not being complete even after repeated evaporations to dryness with a large excess of hydrochloric acid.

Before settling on the plan I now adopt, an easy method was sought for separating the alkalies from magnesia by converting the two into carbonates-a plan that had previously

been adopted; but the question with me was to change the nitrates to carbonates. The idea suggested itself of heating the nitrates with an excess of oxalic acid to the temperature at which the latter undergoes decomposition, when the nascent oxide of carbon might break up the constitution of the nitric acid, and the carbonic acid formed combine with the bases.

On making the experiment I was surprised to see an abundant evolution of nitrous-acid vapors at a temperature considerably below 212°. It was clear that the oxalic acid decomposed the nitrate, liberating the nitric acid, which reacting on the excess of oxalic acid gave rise to the nitrous acid vapors. If crystallized oxalic acid and the nitrate of potash or soda, the former in excess, be placed together in a flask and heated over a water-bath, the mass soon enters into watery fusion, and at the temperature of from 130° to 140° bubbles of gas are evolved, consisting of nitrous acid and carbonic acid. At 212° the evolution is vigorous; and if after evaporation to dryness the water be renewed several times, the nitric acid will be completely expelled from the niter, there remaining the excess of oxalic acid and the oxalate of the alkalies.

It was natural to conclude from the above result that oxalic acid would likewise decompose the chlorides of the alkalies, and on experiment the conclusion proved to be correct. If an excess of oxalic acid be mixed with either the chloride of potassium or of sodium, and the whole warmed gently, abundant vapors of hydrochloric acid are evolved, and by careful manipulation all the chlorine may be driven off under this form.

If heat be applied to the mass resulting from the action of oxalic acid on either the nitrates or the chlorides, all the Oxalic acid will be expelled and the oxalates converted into carbonates. A small amount of chloride of sodium can in this way be converted in a few moments into carbonate of soda; not, however, without some trace of the chloride being present. It is not my object to point to any special application of this decomposition, but it is one that may come into play in certain operations in analytical chemistry.

Experiments were made with the sulphates of the alkalies to see if the oxalic acid had any decomposing action on them, expecting to test for free sulphuric acid by the action of the solution of the mass on zinc or iron, taking for granted that

the presence of oxalic acid alone would not cause the evolution of hydrogen gas. Experiment, however, showed that this manner of testing the question was fallacious, and no other method suggesting itself it was impossible to decide the question positively. Sufficient was ascertained to show that if the sulphate was decomposed it was only to a very minute extent.

In connection with this last experiment it is proved that zinc decomposes water readily in presence of oxalic acid, hydrogen gas being evolved. The action ceases in a short time from the formation of insoluble oxalate of zinc. With iron the action is very feeble even when the solution is heated.

The decomposing action of oxalic acid on the nitrates and chlorides of alkalies appears to be due simply to the fact of a more stable acid being able to replace a more volatile one, and in no way measures the relative strengths of the acids; it being a well-established fact that the physical as well as chemical properties of acids have much to do with their capability of replacing each other, a mere change of circumstances often reversing their relative action.

« PreviousContinue »