RECORD: Schweitzer, Edward G. 1839. Analysis of Sea-water as it exists in the English Channel near Brighton. Philosophical magazine and journal pp. 51-60.
REVISION HISTORY: Transcribed (single key) by AEL Data 10.2008. RN1
X. Analysis of Sea-water as it exists in the English Channel near Brighton. By G. SCHWEITZER*, M.D.
BEING unaware of the existence of a correct analysis of sea-water as it exists in the British Channel, particularly with reference to the quantity of iodine and bromine it contains, I have undertaken at the request of several friends to analyse it. It is not my intention to enter into the minutiæ of the process employed, particularly as I have on a former occasion, in a small pamphlet entitled "An Analysis of the Congress Spring of Saratoga in America," published in March 1838, given a detailed account of the mode I adopt in analysing mineral waters. The chief object I have in view in the present communication is, to explain the method I have employed in ascertaining the proportion of iodine and bromine contained in a given quantity of sea-water. But before I enter upon the subject, it may not be out of place to show how far tests act upon iodine when in connexion with an
* Communicated by the Author.
alkali, and in a solution also containing bromides and chlorides.
From experiment I have ascertained that a minute quantity of iodine in distilled water, equal to no more than 1,500,000th part of the whole, will be distinctly indicated when mixed with starch, dilute sulphuric acid, and chlorine.
For the production of such delicate reaction, I add to every 500 grains of fluid one drop of diluted sulphuric acid, a small quantity of paste of potato starch, and two drops of a weak solution of chlorine, consisting of one part of a saturated solution diluted with 20 to 25 times its volume of distilled water. The solution gives no indication of the presence of iodine in the fluid until a sufficient time has been allowed for the separation of the starch, when a decided pink hue will be visible on the surface of the precipitate if iodine be present. It has been supposed that the substitution of pink for blue in the iodide of starch produced arises from the presence of bromine; but this I have ascertained is not correct, as it depends entirely on the minute quantity of the precipitate acted upon by free chlorine or bromine. The following experiment will prove this fact. In order to ascertain the delicacy of electrolytic tests of iodine, a current of electricity produced by voltaic induction was passed through a suitable glass tube, filled with 300 grains of distilled water containing 1/500,000th part of its weight of iodide of potassium and a small quantity of starch, but no action was observed until a few drops of nitric acid were added, which assisting the electric current, developed, after a few brisk revolutions of the coils of the magnet, the blue colour of the iodide of starch. Even a current of electricity from a single constant galvanic battery passed through the same glass tube, in which the proportion of iodide of potassium was only one millionth part of the weight of the water, indicated the presence of iodine by a pure blue speck of iodide of starch at the anode or negative extremity of the electric circuit. When iodide of potassium diluted in the same manner was properly treated with starch, sulphuric acid, and chlorine, the blue iodide of starch likewise became visible, but the smallest additional proportion of chlorine occasioned a pinkish sediment. The presence of chlorides and bromides, however, do not interfere with the action of the electric current upon traces of iodine; for a solution of salts containing, in 500 grains of water, 100 grs. of chloride of sodium, 10 grs. of bromide of sodium, and the five hundred thousandth part of iodide of potassium gave a deposit of iodide of starch of a dark pinkish colour. A concentrated solution of bromide of sodium, containing the millionth part of iodide of potassium,
also gave by the action of the electric current a slightly pinkish deposit.
It is always necessary, when we wish to detect by means of chlorine minute quantities of an iodide, to employ the chlorine in a very diluted state, as when in excess it forms a soluble chloride of iodine which will not act on starch.
The sulphates and chlorides present in salt waters do not interfere with the delicacy of the starch test; on the contrary a concentrated solution of the chlorides will show the presence of one millionth part of iodide of potassium more distinctly than an equal volume of distilled water. This appears to arise from the iodide being a little soluble in pure water. I thought at first that a trace of an iodide might be contained in the common chloride of sodium, and thus cause a deeper tinge of blue colour; but by employing a chloride of sodium prepared from pure hydrochloric acid and pure soda, I found the same degree of increased reaction. The iodide of starch will likewise keep unchanged much longer in a solution of chlorides exposed to light and air than in pure water.
The bromides when present in large quantity interfere with the delicate reaction upon traces of iodine, but when the quantity of iodine is not too small the reaction is very distinct, as a small proportion of free bromine will, like chlorine, decompose the iodide, and produce the characteristic reaction.
After these experiments I tested fresh sea-water for iodine in the manner before described, but did not obtain the slightest indication of it. I now added one millionth part of the iodide of potassium, and the colour produced by the test did not differ in the slightest degree from a solution of chlorides of the same specific gravity as sea-water, treated in the same manner, and from this I immediately inferred, that iodine, if present in sea-water, must be so in very minute quantity.
I took 73 pounds troy, of sea-water and boiled with a quantity of caustic potash, sufficient to precipitate the alkaline earth, and after filtration evaporated the fluid to four ounces. On testing a small quantity of this concentrated water no iodine was to be detected, and it was found on adding a minute quantity of an iodide that the presence of bromides in comparatively large quantity interfered with the test. But although these results appeared to negative the presence of iodine, I felt convinced it must exist in sea-water, being present in so many sea plants and animals.
Sarphate, in his "Commentatio de Iodio," 1835, Lciden (a treatise which received the prize), states that he could detect no iodine in the sea-water near the Dutch coast. Professor
Charles Daubeney likewise mentions, in his "Memoir on the occurrence of iodine and bromine in certain mineral waters of South Britain, May 1838," that he could not detect iodine in the residuum of sea-water taken from the English Channel near Cowes, after having reduced ten gallons to less than half an ounce.
To proceed with my experiment, I freed three ounces as much as possible from the chlorides by crystallization, having first carefully neutralized the solution with hydrochloric acid. The residuum was then evaporated to dryness, ignited, and treated with anhydrous alcohol. The alcoholic fluid was afterwards evaporated, and the dry residue dissolved in a few drams of water, when the before-mentioned test readily indicated a slight trace of iodine.
With respect to the quantity of iodine in sea-water, it is evidently very minute, 174 pounds troy not containing one grain. This is remarkable when we consider the comparatively large quantity of iodine and bromine present in sea plants and animals, hence we must conclude that these principles are concentrated by vital action.
Bromine when present in fluids is easily detected by chlorine, which produces a yellow colour. If present in very minute quantity the fluid must first be concentrated. But when iodine is present we cannot apply this test, as bromides and iodides are both decomposed by it; and we cannot separate them, even by means of æther, as iodine is soluble in that menstruum, and also possesses greater colouring properties than bromine. From these causes this test is useless when iodine is present, and is only certain when we are previously assured of the absence of that substance.
The following process for the separation of iodine, chlorine, and bromine in fluids containing these substances in very small quantities has given me satisfactory results, as I had anticipated by previous experiment. The fluid while boiling was mixed with a sufficient proportion of caustic potash; my object in this was to decompose the earthy salts, and at the same time prevent the iodine and bromine from being dissipated by heat. The filtered fluid was then evaporated to dryness and ignited, and the resulting mass, after having been dissolved, concentrated, and neutralized with hydrochloric acid, was carefully mixed drop by drop with an ammoniacal solution of chloride of silver prepared by mixing one part of a saturated solution of recently precipitated chloride of silver in ammonia with one of liquid ammonia (sp. gray. 0·935) and two parts of water. If to a concentrated solution of chloride of sodium containing one thirtieth part of a bromide, we add
a few drops of this ammoniacal solution of chloride of silver, the solution will remain clear; but if the most minute particle of an iodide be present, it will be rendered turbid.
To the fluid under examination I added gradually, drop by drop, the solution of ammonia chloride of silver, leaving time between each successive addition for the precipitate of iodide of silver to subside. It is well when bromides are present to keep the vessel closed during the process, otherwise it is of no importance. The iodide of silver collected upon a small filter was first washed with a little diluted ammonia, and afterwards with a few drops of diluted hydrochloric acid to dissolve any earthy substance which the precipitate might contain, and ultimately with pure water.
The filter with the precipitate was dried and ignited. This experiment, repeatedly performed, yielded the most satisfactory results. It requires time, but this is more than balanced by its accuracy. Thus, for instance, I obtained by the analysis of the Congress spring of Saratoga, from 100,000 grs. of the water, 0·12164 gr. of iodide of silver, representing in 1000 grs. of the mineral water, 0·00067 gr. of iodine.
The ammoniacal fluid, separated from the iodide of silver, was carefully evaporated to expel the ammonia, whereby a small precipitate was obtained, consisting of bromide of silver, which was added to that subsequently obtained. This precipitate was formed by the solution of the chloride of silver, more of which was added than was required for the separation of the iodine. That this minute precipitate consisted of bromide of silver, was proved by heating it in a test tube with concentrated sulphuric acid, whereby it became of a delicate yellow colour; whereas chloride of silver would have remained white, and iodide of silver would have obtained a brown colour by parting with its iodine.
A small portion of the fluid may now be examined for bromine, and, when present, the following process may be adopted, which is the same I employed for the separation of bromine in sea-water and brine-springs, where the quantity of chlorides is comparatively very large. The concentrated solution freed from the iodine was introduced into a glass ball, having at its lower end a glass tube, and at its upper an aperture closed by a glass stopper. A concentrated aqueous solution of chlorine was added as long as any sensible yellowness was caused by its addition. The fluid was then agitated with pure æther; and after this had collected on the surface, carrying with it the bromine and chlorine, the water was allowed to flow off through the tube below, and by careful manipulation the æther could then be freed from the water, which
was again treated with æther, lest any bromine should still remain in it. The æther was directly introduced into a glass bottle, containing a solution of caustic potash fully sufficient of discolour the æther, when after evaporation and ignition it was dissolved in water, and carefully neutralised with hydrochloric acid. The concentrated solution was mixed with a few drops of an ammoniacal solution of chloride of silver prepared thus: one part of a concentrated solution of chloride of silver in ammonia, mixed with one part of ammonia and one part of water. A few drops of this mixture produced no turbidness in a solution of chloride of sodium, but indicated a very minute quantity of bromine. When no further turbidness was produced by an additional drop of this ammoniacal solution of the chloride of silver, the fluid under treatment, which was kept in an open vessel, was heated in a sand-bath until the ammonia was almost evaporated. A few drops of the test were again added, until it no longer produced turbidness, when the glass vessel was again placed in a sand-bath, until the fluid, after having been heated, gave no further indication of bromine; it was then tested again with chlorine. When the proportion of the chlorides to the bromides is not too large, scarcely a faint yellowness will be produced; if, however, it is, the bromine must again be separated by chlorine and æther, and the before-mentioned process repeated, when the last traces of bromine will be separated as bromide of silver, which is to be treated like the iodide of silver before it is weighed. In this manner I have been able to detect the smallest proportion of an iodide and bromide when accompanied by a great quantity of chlorides, and have also been enabled to separate them and to ascertain their respective quantities. Should the quantity of iodine be much larger than that of bromine, it would be requisite to evaporate a little of the ammonia; and although the addition of the ammoniacal solution of chloride of silver, employed as a test for iodine, no longer produces turbidness, it is still necessary to add another drop of the precipitating fluid, in order to ensure the separation of every trace of iodine. This is the more important, as the iodide of silver is not entirely insoluble in ammonia; and although the quantity dissolved might be exceedingly minute, still this repetition is necessary in an accurate analysis. The same precaution must be observed in the separation of bromine, as bromide of silver is to some extent soluble in ammonia, for it is obvious that by the addition of the ammoniacal precipitant for every portion of bromide of sodium or potassium, an equivalent of bromide of silver and chloride of sodium or potassium will be formed, and the
corresponding quantity of ammonia, which kept the chloride of silver in solution, will be free and act upon the bromide of silver; but by observing the before-mentioned precaution, every error of that kind will be avoided. Should a fluid contain iodides and bromides without chlorides, and not in too small a proportion, a very good method of ascertaining their respective quantities is to precipitate them at once with nitrate of silver, and to heat the dry precipitate in an atmosphere of bromine. I have found, when iodide of silver is melted in an atmosphere of bromine, it is entirely changed into a bromide; and from the difference of the weight between the mixture of iodide and bromide of silver, and that of the whole bromide of silver, the respective quantities of iodine and bromine may be ascertained. Thus the quantity of iodine (or bromine) stands in proportion to the difference of the weight, as the atomic weight of iodine (or bromine) is to the difference of their atomic weights. Hence it would only be required for the quantity of iodine to multiply the given difference of the weight by 2,627, and for that of bromine to multiply it by 1,627. Professor H. Rose, of Berlin, applies a similar method for the separation of iodine from chlorine.—(Poggendorff's Ann. 1834, No.37, p. 583, 584.)
I may appear to have dwelt long upon this subject, but the importance into which brine springs have arisen on account of their powerful components, iodine and bromine, has induced me to examine the matter closely, as it may be of consequence to the medical profession to know the exact quantity of these valuable substances.
I have briefly to add, that the quantity of chlorine in sea-water was ascertained by means of nitrate of silver, deducting from it that proportion of bromine which had been found according to the foregoing method. The quantity of sulphuric acid was found by chloride of barium, the water having previously been mixed with a little nitric acid. Another portion of the water was mixed with chloride of barium without the addition of an acid, when the difference of the weight between this and the former precipitate gave the amount of carbonate of barytes from which the proportionate quantity of carbonic acid gas was computed; its quantity was likewise ascertained after the distribution of the acids amongst the bases, when the surplus of the lime or of one of the other bases must have been united to carbonic acid. The quantity obtained by analysis was a little less than the last, owing to the carbonate of barytes not being entirely insoluble in water during lixivation. Lime was separated by oxalate of ammonia, the water having been previously mixed with a proper
quantity of chloride of ammonium. After the separation of lime, magnesia was precipitated by the addition of ammonia and phosphate of ammonia.
The precipitate was washed with water containing 10 per cent. of ammonia, whereby the solution of the precipitate was prevented. After the sea-water had been freed from the earthy chlorides and sulphates by hydrate of barytes and carbonate of ammonia, it was evaporated to dryness, and the residue heated to redness, and weighed. The alkaline chlorides were dissolved in water mixed with perchloride of platinum, and evaporated to dryness. The residue digested with spirits of wine containing 60 per cent. alcohol, left potassio chloride of platinum, which was dried, weighed, and computed as chloride of potassium. The surplus of the total amount of the alkaline chlorides will give the precise quantity of the chloride of sodium.
The equivalent numbers have been computed according to the Tables which H. Rose has affixed to his Handbuch der analytischen Chemie. Zweiter Band.
I subjoin by way of comparison an analysis of the Mediterranean by Laurens. (Journal de Pharmacie, xxi, 93.)
|Sea-water of the British Channel.||Of the Mediterranean.|
|Chloride of sodium||27·05948||27·22|
|— of potassium||0·76552||0·01|
|— of magnesium||3·66658||6·14|
|Bromide of magnesium||0·02929||—|
|Sulphate of magnesia||2·29578||7·02|
|— of lime||1·40662||0·15|
|Carbonate of lime||0·03301||Carb. of lime & magnesia.||0·20|
When these analyses are compared, it will be found that the Channel water contains 9 times as much lime as the Mediterranean, but this can be accounted for, as the water flows over a bed of chalk. The Mediterranean again has twice as much magnesia and sulphuric acid.
We also find that the English Channel contains in 1000 grains water, 35·25628 grains of anhydrous ingredients; which amount corresponds very nearly to 35 grains, or 35·1 grains, obtained from several experiments, when 1000 grains were evaporated in a platina crucible, mixed with a little chloride of ammonium, to prevent as much as possible the decomposition of the earthy chlorides, and the residue care-
fully ignited, in order to volatilize the chloride of ammonium, where, however, a dissipation of hydrochloric acid had taken place.
Sometimes I found faint traces of oxide of iron, when the concentrated water was mixed with sulphocyanuret of potassium, particularly after boisterous weather; I found the same in respect to organic matter. The sea-water taken on a fair and calm day, when very transparent, did not yield the slightest indication of extractive matter when evaporated and ignited. A small quantity of free carbonic acid gas has been likewise found; and also extremely minute traces of chloride of ammonium were detected, when about 5 pounds of sea-water were evaporated in a water-bath to nearly half an ounce, which, mixed with caustic soda, produced fumes close to a glass rod wetted with hydrochloric acid.
Sea-water has been likewise examined for silica, alumina, strontia, manganese, phosphoric acid, and nitric acid, none of which could be detected.
The sea-water used for the occasion was taken on the 3rd of June, from the surface six miles from the shore, at high water. The weather was fair, the sea calm and extremely transparent. Its specific weight was at 60° Fahr. 1·0274. Another portion obtained by a proper apparatus from the very bottom of the sea, 10 fathoms deep, was of the same specific gravity, and likewise that taken almost close to the shore. In the month of July, after a previous rainy day, the sea-water taken four miles from the shore, had at 60° Fahr. a specific gravity of 1·0274; at a distance of 2 miles, 1·0271; and close to the shore, 1·0268. It was examined several times in August, the weather being fair and warm, when the specific gravity amounted to 1·0274. This appeared to be the greatest weight.
When weighed in fair weather in December, it was almost 1·0271; after rain I found it to be 1·0267. These variations will of course depend entirely on the state of the weather. If the atmosphere be bright, and no heavy rain has lately fallen, the water will have, even close to the shore, the same specific weight as out at sea, but after rain it is obvious that the sea-water close to the shore will be most diluted. It is therefore indispensable that the sea-water for examination should be taken at a distance of several miles, that its specific weight should be ascertained, and that the analysis should be performed from one and the same dip.
I cannot conclude this paper without drawing the attention of medical men to the importance which the brine springs on the Continent have lately acquired, as, for instance, the springs
near Kissingen, the Adelheids quelle, near Heilbroun, and above all, the springs of Kreugnach, which have been found highly beneficial in scrophulous diseases when internally administered, their action being dependent entirely on the chlorides, iodides, and bromides then contain. Sea-water would afford similar advantages for bathing, and when evaporated to dryness, the residue might be kept in earthen vessels, and thus be conveyed to any distance; and as its constituents are very soluble, sea-water in perfection might be procured at any place. The evaporation of sea-water should be performed with care, and the ingredients kept by chemists. One great advantage would accrue from this method, viz. that sea-water could be had of any degree of concentration which the practitioner might deem necessary. At the baths of Kreugnach, for example, extraordinary effects have been produced when from 40 to 70 quarts of the mother liquor were added to the natural salt-water of that spring, and this mixture used for bathing.
German Spa, Brighton, June 1839.
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