« PreviousContinue »
CHROMATE OF POTASSA:
A RE-AGENT FOR DISTINGUISHING BETWEEN THE SALTS OF BARYTA AND STRONTIA.
Having had occasion some months since to examine a specimen of fibrous celestine from Niagara, I was led to suspect from its specific gravity that baryta was present.
With this supposition I examined for baryta, in the usual way, with fluo-silicic acid; in fact, the only certain method. that I was aware of. The indication that this test gave of its presence was so unsatisfactory that it led me at once to search for a more decisive and more delicate distinguishing test, and the following was the result of my labor.
It will be needless to detail the various re-agents that I had recourse to in my experiments, but suffice it to say chromate of potassa satisfied my most sanguine wishes, for no re-agent with which I am acquainted acts so promptly upon any body as does this upon the salts of baryta; and moreover, so delicate is this test that in one of my experiments, in which a grain of chloride of barium was dissolved in one gallon of water, it gave immediate indication of the presence of baryta, although sulphuric acid failed to do so; in fact, it will affect perceptibly a solution that contains less than one hundred-thousandth part of baryta.
When a strong solution of chromate of potassa is poured upon a strong solution of a salt of strontia a precipitate (similar to that which is produced when a salt of baryta is used) will take place. Solutions of these two salts of ordinary strength will not affect each other.
Lest this fact should, under any circumstance, cause erroneous conclusions, I sought for some acid which would dissolve the one precipitate and not the other. Acetic acid is the only acid among the many that I have tried which answered this end. If a small quantity of dilute acetic acid (common acetic
acid diluted with five times its weight of water was used) be poured upon the precipitate produced in the case of strontia, it will be completely dissolved; whereas no impression is made on that from the salts of baryta.
Acetic acid, so concentrated as to crystallize when its temperature was below 50°, was poured on the precipitated chromate of baryta, and a portion of it taken up, but in no instance did any quantity of the acid dissolve the entire precipitate.
With the above means there need not now remain the least doubt in ascertaining promptly the presence of baryta in a salt of strontia supposed to contain it; for all that is necessary to be done is to add to a solution of the salt a solution of chromate of potassa, which, if baryta be present, will produce a lightyellow precipitate insoluble in acetic acid. This re-agent will also serve to distinguish baryta from lime.
BISULPHATE OF SODA AS A SUBSTITUTE FOR
THE BISULPHATE OF POTASH
IN THE DECOMPOSITION OF MINERALS, ESPECIALLY THE ALUMINOUS MINERALS.
In referring to the more recent works on analytical chemistry I perceive that the bisulphate of potash is still used to the almost utter exclusion of bisulphate of soda in rendering certain minerals soluble and it is still recommended as the proper agent to fuse with aluminous minerals, as corundum, emery, etc.
This subject occupied my attention to a considerable extent when engaged in the preparation of two memoirs on the geology and mineralogy of emery, presented to the French Academy of Science in 1850, as well as in some investigations I am now making on the emery from Chester, Mass. In the above researches I had a large number of corundums and emeries to analyze. The powdered minerals were fused with the bisulphate of potash in the usual way, and I found no difficulty in decomposing the minerals; but unfortunately during the operation a double salt of potash and alumina is formed which is almost insoluble in water or in the acids, and it is only by a solution of potash that it is first decomposed and afterward redissolved. There are many disadvantages and delays attendant upon this method which experience soon exhibits, as the constant deposition of alum if the solution is not kept quite dilute. I therefore experimented with the bisulphate of soda, knowing that the double salt of alumina and soda was quite soluble, and my results were every thing that could be desired; for while the soda-salt gives a decomposition at least as complete as the potash-salt, the melted mass is very soluble in water, and in the future operations of the analyses there is no embarrassment from a deposit of alum. The manner of employing the bisulphate of soda in the analysis of emery is referred to in the article on the emery of Chester, Mass.
PREPARATION OF THE BISULPHATE OF SODA.
The ordinary commercial article is not sufficiently pure for use, and I prepare it from pure carbonate of soda or sulphate of soda that has been purified by recrystallization. In either instance pure sulphuric acid is added in excess to the salt in a large platinum capsule, and heated over a flame until the melted. mass, when taken up on the end of a glass rod, solidifies quite firmly. The mass is then allowed to cool; moving it over the sides of the capsule will facilitate this operation. When cool it is readily detached from the capsule, then broken up, and put into a glass-stoppered bottle. So far as my experience has yet gone, in almost every instance where we have been in the habit of using bisulphate of potash, the bisulphate of soda can be substituted.
ACTION OF POTASH UPON CHOLESTERINE.
For some reasons we would be induced to place cholesterine among the fatty bodies, but from many of its characters it would appear certainly not to belong to this class of bodies. The most important distinctions between these two bodies are, first, the want of action of a solution of potash upon cholesterine; and secondly, its high point of fusion, which is 298° Fah.*
Another difference which I am able to point out is that cholesterine is heavier than water, whereas the fats are lighter. It will be found in works on chemistry that cholesterine is lighter than water, and I attribute this to the fact that the substance, as it crystallizes out of alcohol, was found to float on the surface of water; but this is owing to the air adhering to the crystals. To show that it is heavier all that is necessary to be done is to throw a small piece of fused cholesterine into a vessel containing water, that must afterward be made to boil (this is done to drive away the air adhering to the surface of the body); after which it will be found to sink, and remain at the bottom of the vessel even when the water is cold. I dwell thus much upon this because I feel confident that there are other organic bodies that are said to be lighter than water, but which are actually heavier; for, owing to the looseness of their structure, air insinuates itself between the molecules, and is afterward held so firmly that it is impossible to drive it away by the ordinary means. I now return to the first distinguishing character between cholesterine and the fats-the difference of the action of potash upon the two bodies.
Chevreul and others have shown that if cholesterine be digested a great length of time in a boiling solution of potash no change takes place; but here the cholesterine is not subjected to the action of the potash under the same circumstances
* The melting-point of most of the fats is below 140°.