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Part I--General Discussion of Mineral Waters, continued
Chapter VI--Methods of Analysis, of Calculation, and of Stating Results
Methods of Analysis
Total Solids
This determination is made by evaporating from 100 cc. to 500 cc. of the water to dryness on a water-bath in a weighed platinum dish, and then, heating the residue to 130° C. in the air-bath. The presence of various hygroscopic salts may cause this result to be more or less dependent on the quickness with which the weight is made. The result is of special use as a "control" test, so this determination is never neglected. It is sometimes advisable, after weighing, to ignite the dried residue, so as to notice if an appreciable blackening takes place. This blackening would indicate the presence of large quanties of organic matter.
Determination of Bases
The analysis for those bases that are most abundant is made by using a fresh sample of water, from one to ten liters, dependent on the amount of total solids obtained above, acidulating it with hydrochloric acid, and evaporating to dryness on the water-bath. The evaporation may be hastened by boiling gently at first in a porcelain evaporating dish, and adding measured quantities of water from time to time, and completing the operation on the water-bath. The residue is either heated on the water-bath till every trace of odor of hydrochloric acid is gone, or it is heated to 110° C. on a water-bath for some time. After moistening the residue with hydrochloric acid and digesting, water is added, and the solution is filtered. It is of the utmost importance to note at this stage that in the presence of notable quantities of calcium sulfate, a single treatment in this way is not sufficient, but the residue should be boiled several times, with dilute hydrochloric acid and water.
Silica and Insoluble Residue is the term applied to the above precipitate. After this is weighed, it may be tested for purity by heating with hydrofluoric acid. If any residue remains after this treatment, it should be tested for barium sulfate and other constituents by fusion with sodium carbonate.
For Iron and Aluminum Oxids, the filtrate from the silica and insoluble residue is treated by the ordinary methods, using ammonium chlorid and ammonium hydroxid. If the amount of this precipitate is considerable, the precipitate should be redissolved and again precipitated, using the same filter for collecting the precipitate the second time, and combining the filtrates. This precipitate, in addition to the above oxids, may contain phosphoric anhydrid, in case a qualitative examination has shown that to be present in the water. To determine the iron, after weighing, dissolve the precipitate in concentrated hydrochloric acid by digesting for some time, and determine the iron volumetrically in a sulfuric-acid solution by the ordinary methods. If phosphoric anhydrid was present, that should. be determined in a separate sample of the water. The sum of this oxid and ferric oxid substracted from the total precipitate is calculated as alumina.
For the determination of Calcium, the filtrate from the iron and aluminum hydroxids should be treated with ammonium oxalate, and the solution should be kept warm for some time. In case much magnesium is supposed to be present, it is best to dissolve the precipitated calcium oxalate in hydrochloric acid and precipitate a second time, combining the filtrates. Calcium may be weighed as oxid or sulfate.
As Magnesium still remains in the filtrate from the calcium, evaporate this filtrate to dryness with an excess of nitric acid in a porcelain evaporating dish, and finally heat over wire gauze. By this treatment, in ordinary waters the ammonium salts will nearly all be converted into ammonium nitrate, which, at a higher temperature, is broken up into nitrous oxid and water, both of which are readily volatile. In this way the excess of ammonium salts, which would interfere with the complete precipitation of magnesium, is nearly all removed. The residue is dissolved in water acidified with nitric acid, filtered if necessary, and treated with a few drops of ammonium chlorid, then with ammonium hydroxid and sodium hydrogen phosphate, by the ordinary methods.
For the determination of Sulfuric Acid, a fresh portion of the water, from 100 cc. to 1000 cc., is acidulated with hydrochloric acid, filtered if necessary, and evaporated somewhat, if the amount of sulfuric acid is small. The solution is heated to boiling and treated with as small a quantity of hot barium chlorid solution as possible to insure complete precipitation, and after standing for some time the precipitate of barium sulfate is filtered off, After weighing, as this precipitate is so liable to carry down with it other barium salts, it is boiled with hydrochloric acid, and, after the addition of water, filtered, ignited, and again weighed.
For the determination of Potassium and Sodium, the filtrate from barium sulfate is evaporated to dryness with hydrochloric acid, and silica is separated as usual. The solution is then treated with barium hydroxid, and, after standing for some time, is filtered. The filtrate is concentrated to small bulk and ammonium carbonate is added and the solution is again filtered. The filtrate is evaporated to dryness in a platinum vessel, and the residue is ignited at a low temperature. A few drops of water are added to the residue and a small piece of solid ammonium carbonate is added, and the solution is allowed to stand for a short time. In case a precipitate, which would be carbonates of alkaline earths, is obtained, filter off, and evaporate the filtrate to dryness and again heat cautiously, and weigh. The residue consists of chlorids of the alkalies, and may be examined for the individual alkalies by well-known processes. If lithium has been found by a spectroscopic test, a larger quantity of water must be used and a special determination of lithium made.
For the determination of Sodium Carbonate, a liter of the water is evaporated on a water-bath to dryness, distilled water is added, and the solution is filtered, with slight washing of the precipitate. The filtrate contains the sodium carbonate, which may be estimated by the ordinary alkalimetric methods.
The amount to be used for the estimation of Chlorin depends upon the quantity of chlorids in the water. For ordinary waters from 200 cc. to 500 cc. is sufficient, and, in the latter case, it is advisable to concentrate the water by boiling, first making the water exactly neutral by sodium carbonate, in case it has an acid reaction. Determine the chlorin by titration with a standard solution of silver nitrate, observing that the water should be made exactly neutral before titration.
In the estimation of Lithium, the method suggested by Gooch was followed (see Leffmann and Beam's "Examination of Water for Sanitary and Technical Purposea."). To the concentrated solution of the weighed chlorids of sodium, potassium and lithium amyl alcohol was added, and heat applied gradually, until steady boiling was effected (about 270° F.) This precipitates the potassium and sodium chlorids, and dissolves the lithium chlorid. To the cooled liquid two drops of strong hydrochloric acid were then added, and the boiling repeated. The solution was allowed to settle, and decanted through a filter, and the filtrate measured. The residue was washed with dehydrated amyl alcohol, and the washings added to the filtrate after measurement of the former. The filtrate and washings were evaporated in a platinum crucible to dryness, converted to sulphate, heated to fusion, cooled, and weighed. Prom this weight was subtracted for each ten cubic centimeters of the filtrate .0005, .0006 or .0010 grams, according as only sodium chlorid, potassium chlorid, or both, were present in the amyl alcohol filtrate. The presence of lithium in the sulfate residue was in each case confirmed by the spectroscope. Special evaporations of at least a liter of the waters were made for the lithium determinations.
For the determination of Barium and Strontium, the following method has been found to be very satisfactory (condensed from Cairns's Qnantitative Analysis, pages 296-298): "Evaporate from five to fifteen liters of the water nearly to dryness, filter, and wash. The residue will contain barium and strontium as carbonates and sulfates, and the filtrate may be used for the determination of brominv.iodin , and boric acid. The residue is treated with hydrochloric acid, evaporated to dryness, as in the separation of silica, and the insoluble residue is filtered off. Call this filtrate 'solution B.' The residue last mentioned is heated with hydrofluoric acid to expel silica, and then fused with sodium carbonate. The fused mass is dissolved in water, and the precipitate, which would contain the barium and strontium as carbonates, is dissolved in hydrochloric acid and added to solution B. This solution, with solution B, is treated with sulfuric acid to precipitate the sulfates of barium and strontium, the precipitate is ignited and fused with sodium carbonate, digested with water, and filtered. The insoluble part is treated with acetic acid, and in this solution the barium is precipitated with potassium chromate. This precipitate, after being filtered off, is digested with sulfuric acid, and finally weighed as barium sulfate. The filtrate from the barium chromate is digested with ammonium carbonate, and the strontium carbonate, with a little calcium carbonate, is filtered off. This precipitate is dissolved in nitric acid and evaporated to dryness in a weighed platinum dish. The solid residue thus obtained is digested with a mixture of equal parts of absolute alcohol and ether, which will dissolve the calcium nitrate without having any appreciable action on the strontium nitrate. Weigh the residue as strontium nitrate in the platinum dish. Test all the residues with the spectroscope."
For the determination of Boric Acid, an excellent method is that suggested by Gooch (Am. Chem. Jour., IX, 23; also, Cairns's Quant. Anal., p. 299). In this process the dried salts are treated in a retort of special construction, which can be heated in a parafine bath, with acetic acid and methyl alcohol, and the latter on being distilled off carries with it the boric acid. This acid is then caught in a known weight of calcium hydrate, and after the operation the calcium oxide is heated and determined. The increase in weight of the lime is due to the boric anhydrid (B2O3) that has been absorbed.
For the determination of Fluorin (Cairns's Quant, Anal., p. 301), a large quantity of the water is concentrated, and precipitated with calcium chlorid, and after filtration the ignited precipitate is treated with acetic acid to dissolve the carbonates. The residue which contains the fluorids is dried, and mixed with pulverized quartz and concentrated sulfuric acid, and heated. The loss in weight is the hydrofluric acid which has been volatilized.
In order to determine Sulfur (Erdmann's Journal, vol. LXX, or Cairns's Quant, Anal., pp. 302-304), which may be present as sulfids, hyposulfites, or free hydrogen sulfid, the water must be treated at the springs for each of the ions supposed to be present. The sulfur existing as free hydrogen sulfid gas and as sulfids may be determined by treating a known volume of the water at the spring with an acid solution of cadmium clorid, and, after filtration, determining the cadmium by the usual methods.
For the quantitative determination of Chlorin, Bromin, and Iodin (Journal of the British Chemical Society, vol. 49, p, 682, M. Dechan), the mixture of the evaporated salts is placed in a flask of 250 cc. capacity with 40 grams of potassium dichromate and enough water to make 100 cc., counting the water in which the halogens were dissolved. The flask is provided with a dropping funnel through which water may be added to keep the volume of the solution above two-thirds and not more than the original amount. The flask is also connected to a vertical condenser, which condenses the steam and halogen vapors. The halogen vapors are received at the lower end of the condenser in a five-per-cent. solution of potassium: iodid. After the mixture has been boiled till the iodin is all distilled, eight cc. of sulfuric acid (equal volumes of sulfuric acid and water) is added through the dropping funnel, and the mixture is again distilled until bromin no longer comes over. The iodin distilled over and the iodin set free by the bromin which was distilled over are each titrated with N/100 thiosulfate solution, and the iodin and bromin calculated from the amount used. The chlorin can be estimated with a silver nitrate solution in the cooled residue in the flask.
For Nitrates, the methods described in the report of the Massachusetts Board of Health for 1890 may be employed.
Methods of Calculation and of Stating Results
It is important to inquire what is the simplest method of stating results in a chemical analysis. We determine so much silica, calcium, oxid, sulfuric anhydrid, chlorin, etc.; so it has seemed to the author best to use what he has termed "radicals;" but even here, if he includes sodium oxid, there is an assumption that this is really the condition in which sodium should be combined. On this account, therefore, if we would state the exact result of the analysis, we can only do so in terms of ions (see chapter V), following practically the report of the committee of the A. A, A. S. (J. Anal. Chemistry, vol. III, p. 398), appointed at the Buffalo meeting.
Ions and Radicals
In stating the results, then, the ions are first reported, then the radicals, calculated from these ions; next, the probable combinations of the basic and acid ions, all in grams per liter; and finally the probable combinations, in grains per gallon. The method of expression by radicals will enable the chemist to better report the relative amounts of each substance found, while, if he wishes to report the actual elements determined, he can find them in the column marked "ions." It is true, in writing the radicals, we have included carbonic anhydrid and water, with the understanding, however, that these are usually "calculated," and not determined.
Now it practically happens that there is considerably more carbon dioxid than is necessary to combine with the bases with which we assume the combination takes place. This is of course due to the well-known solubility of carbonic anhydrid in cold water. In making the list of radicals, we have assumed, as above noted, that a certain amount of oxygen was united with the metals giving us Na2O, K2O, etc.; but we know, in comparing the sum of the individual constituents with the total solid residue, that often a part at least of the sodium was combined with chlorin, for instance, so that the oxygen of these radicals does not really belong there, and should be subtracted. It is true we have made arbitrary comparisons, as some one has said, which cannot be proved. Nevertheless, for convenience of comparison, this method is adopted.
Hypothetical Combination
As it has been the custom among water analysts to report the constituents as being present in definite combination as salts, the "hypothetical combination" has been stated in another column, so as to make the analysis more intelligible to the ordinary reader and to the physician who is not familiar with ions or radicals. This is especially desirable because we can thus compare the analysis of those waters with the analyses of other chemists. The problem in regard to what combination should be made is a complex one, for certain combinations that would take place in a dilute solution do not take place in a concentrated one. If the solutions of two salts are mixed, and an insoluble salt is precipitated by this mixture, then the reaction is a simple one. But how shall we know what takes place when, for instance, solutions of magnesium sulfate and sodium chlorid are mixed? No precipitate is formed. Does the solution contain each salt as originally present, or does a metathetical reaction take place, forming sodium sulfate and magnesium chlorid?
So many factors must be considered in the discussion of this question that we must decline to answer it, positively. We must know the effect of temperature, of concentration, and of other salts in solution, as well as of the relative quantities of each salt present, before we can form a judicial opinion as to what combinations are actually present. If the solutions are dilute no change takes place, and the substances remain as ions. If the solutions are concentrated, all possible salts as well as all the ions will be present. (For a further discussion of this problem in the light of the most modern theories, see chapter V.)
Following the example of most chemists, the results are expressed in terms of grams per liter. This seems to be preferable in the case of mineral waters where the amount of total solids is large, rather than expressing the results in terms of parts per hundred thousand or parts per million, according to the custom in reporting the sanitary analysis of waters. We assume, of course, that grams per liter represents parts per thousand by weight, but this is only true in the case of waters having a very low specific gravity, and to make it absolutely true in regard to all waters examined we must know the actual specific gravity, and take thatspecific gravity into consideration in making our calculations. We have adopted the system of expressing the results in grams per liter, also, looking hopefully to the time when this nation will follow other civilized nations and adopt the metric system as the only legal system of weights and measures.
Grains in a Gallon
It unfortunately happens that in this country people have adopted the habit of representing the composition of mineral waters in terms of grains per gallon. The physician and the ordinary reader who is interested in sanitary matters have become accustomed to this, and they find difficulty in interpreting the results stated in any other way. Therefore, in deference to this fact, results are also expressed in grains per United States gallon of 231 cubic inches, as represented in the last column.
There is, however, unfortunately still a disagreement as to the actual relation of grains per gallon to grams per liter. It is hoped that this disagreement among authorities will be speedily reconciled. As an example of what some of the best authorities have used as a factor to express this relation, it is noticed that Professor Mason has used the factor 58.3349, Professor Chandler 58.318, Dr. A. C. Peale, of the United States Geological Survey, prefers 58.41, Prof. W. R. Nichols has used 58.37, Prof. Paul Schweitzer in his late report (Mo. Geol. Surv., vol. III, Mineral Waters) recommends 58.41, and Professor Brockett uses the factor 58.372.
In the calculations in this volume the factor 58.41 has been employed.
Table of Factors Used in Water-Analysis Calculations, by D. F. McFarland. Multiply the amount found by the factor to obtain the amount sought of the corresponding substance. Whole numbers, except 35.4 for chlorin, are used for atomic weights,
| Found | Sought | Factor |
|---|---|---|
| Calcium | ||
| CaSO4 | CaO | .41181 |
| Ca | .29428 | |
| SO3 | .58819 | |
| CaH2(CO3)2 | CaO | .34569 |
| H2O | .11111 | |
| 2CO2 | .54321 | |
| Ca | .2471 | |
| CaCO3 | CaH2(CO3)2 | 1.6200 |
| Ca | .40032 | |
| CaO | .56021 | |
| CO2 | .43979 | |
| CaCl2 | CaO | .5050 |
| 2Cl | .6389 | |
| Ca | .5051 | |
| CaO | Ca | .71459 |
| Ca3(PO4)2 | 3Ca | .13910 |
| Magnesium | ||
| MgSO4 | MgO | .3333 |
| Mg | .2000 | |
| MgH2(CO3)2 | MgO | .2739 |
| Mg | .1642 | |
| H2O | .1233 | |
| 2CO2 | .6027 | |
| MgCO3 | MgH2(CO3)2 | 1.7380 |
| Mg | .2856 | |
| MgO | .4769 | |
| CO2 | .5241 | |
| MgCl2 | MgO | .4219 |
| Mg | .2530 | |
| 2Cl | .7468 | |
| MgO | Mg | .6000 |
| Sodium | ||
| Na2SO4 | Na2O | .43682 |
| 2Na | .32429 | |
| 2NaHCOs | Na2O | .36910 |
| 2Na | .2738 | |
| H2O | .10714 | |
| 2CO2 | .52380 | |
| Na2CO3 | 2NaHCO3 | 1.5849 |
| 2Na | .4347 | |
| 2NaCl | Na2O | .53083 |
| 2Na | .39407 | |
| 2Cl | .60616 | |
| Na2B4O7 | Na2O | .3070 |
| 2Na | .2278 | |
| B2O6 | .6925 | |
| B2O7 | .7725 | |
| 2NaNO3 | Na2O | .3572 |
| N2O5 | .6352 | |
| 2NaBr | Na2O | .3012 |
| 2Br | .7760 | |
| 2NaI | Na2O | .2080 |
| 2I | .8460 | |
| Ammonium | ||
| (NH4)2SO4 | 2NH4 | .2730 |
| Iron | ||
| FeH2(CO3)2 | FeO | .4045 |
| Fe | .3146 | |
| H2O | .1011 | |
| 2CO2 | .4943 | |
| FeCO2 | FeH2(CO32 | 1.5345 |
| Fe | .4868 | |
| FeO | .6201 | |
| CO2 | .3790 | |
| Fe2O3 | 2FeO | .90002 |
| 2Fe | .70008 | |
| 2FeH2(CO3)2 | 2.2250 | |
| FeO | Fe | .7777 |
| FeSO4 | FeO | .4740 |
| Aluminum | ||
| Al2O3 | 2Al | .51300 |
| Manganese | ||
| MnH2(CO3)2 | MnO | .4012 |
| H2O | .1017 | |
| 2CO2 | .4970 | |
| Mn | .3102 | |
| Mn3O4 | 3MnO | .9300 |
| Potassium | ||
| K2SO4 | K2O | .54061 |
| 2K | .44800 | |
| 2KHCO3 | K2O | .4800 |
| H2O | .0810 | |
| 2CO2 | .4400 | |
| 2K | ,3920 | |
| 2KCl | K2O | .63189 |
| 2K | .5240 | |
| 2Cl | .4780 | |
| K2CO3 | 2KHCO3 | 1.4492 |
| 2K | .5652 | |
| K2O | 2K | .8299 |
| Lithium | ||
| 2LiCl2 | Li2O | .3540 |
| 2Li | .0900 | |
| 2Cl | .8350 | |
| 2LiHCO3 | Li2O | .2206 |
| 2Li | .1028 | |
| H2O | .1323 | |
| 2CO2 | .6471 | |
| Li2CO3 | 2LiHCO3 | 1.8378 |
| 2Li | .1891 | |
| Li2O | 2Li | .4670 |
| Acids, Radicals, and Ions | ||
| SO3 | SO4 | 1.2000 |
| SiO2 | SiO3 | 1.2666 |
| B4O6 | B4O7 | 1.1142 |
| 2PO4 | P2O5 | .7470 |
| Oxygen equivalent of |
Chlorin | .22599 |
| Bromin | .10000 | |
| Iodin | .06300 | |
Some of the analyses reported in this volume are by other chemists than those of the Survey, and no definite figures are obtainable as to their methods of calculation. Where they have represented the hypothetical combination, as is usually the case, in terms of grains per gallon, from these figures the grams per liter, using the factor 58.31, have been calculated. The radicals have not usually been calculated in such cases. In several analyses the chemists have made no attempt at even a hypothetical combination, and here only radicals and ions per liter are given.
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