the globe B. This globe is rather more than half filled with sulphuric acid, when the instrument is employed in the analysis of the carbonates. The standard weight of car E D 8 bonate of soda = 24 grains, or of carbonate of potash = 31 grains, is then put into A, having previously laid a minute globe of glass over the lower orifice; the cork, with its small tube, is now firmly adjusted; and the apparatus is weighed in its upright position, either by suspension with a hook to the end of the beam, or by resting it on the scale in a light socket of any kind. It is next laid hold of, and inclined so as to cause a little of the acid in в to pass over into A. Effervescence ensues with greater or less vehemence, according to the nature of the carbonate and quantity of the acid introduced. Should it be too violent, and threaten an overflow by intumescence, it can be instantly abated to any degree by the slightest slope of the instrument. Now, this power of control forms the peculiar feature and advantage of this contrivance; whereas in all other forms of such apparatus that I know, whether by sucking over or pouring in, if a little too much acid comes upon the carbonate, the experiment is effectually marred. The gas disengaged in A must necessarily traverse the sulphuric acid in B, and e stripped of its moisture before escaping into the air. Having supersaturated the alkaline base, and cooled the apparatus, we weigh it again, and the loss of weight in grains and tenths denotes the per-centage of soda or potash, provided their neutral carbonates had been the subjects of experi ment. For limestone, on the same plan of computation, 22 grains may be taken. It deserves to be noted, that the present instrument has only one junction, and needs no chloride of calcium, a substance so apt by its swelling to burst the glass tubes that contain it.* A II. ACIDIMETRY. I have already stated, that water of ammonia of standard strength, faintly tinted with litmus, affords a most exact and convenient acidimeter, when poured or let fall from a graduated dropping-tube. Bicarbonate of potash also, when dissolved in water, so that 1,000 grain measures contain one atom of the salt counted in grains, is a good test-liquor for the same purpose; for if the centigrade measures expended in effecting neutralization are multiplied by the atomic weight of the given acid, the product is the quantity in grains of acid present. Acidimetry may be likewise exactly performed by measuring in the cylindric gasmeter (fig. 6) the volumes of carbonic acid gas disengaged from pure bicarbonate of potas or soda, by a given weight of any acid, taking care to use a small excess of the salt. Thus, for example, 16.8 grains of dry and 20 of hydrated sulphuric acid disengage 10,000 water grain measures of gas from bicarbonate of potash. Therefore, if 20 grains of a given sulphuric acid be poured into the flask of fig. 6, upon about 50 grains of the bicarbonate, powdered and covered with a little water, it will cause the evolution of a volume of gas proportioned to its strength. If the acid be pure oil of vitriol, that weight of it will disengage 10,000 grain measures of gas; but if it be weaker, so much less gas-the centigrade measures of which will denote the per-centage value of the acid. If the question be put, how much dry acid is present per cent. in a given sulphuric acid, then 16.8 grains of the acid under trial must be used; and the resulting volume of carbonic acid gas read on the scale will denote the per-centage of dry acid.f For nitric acid, we should take 22-6 grains; for hydrochloric or muriatic acid, 15-34; for acetic acid, 21-6; for citric acid, 24-6; for tartaric acid, 28 grains: then in each case we shall obtain a volume of carbonic acid gas proportioned to the strength and purity of these acids respectively. The nitric, hydrochloric, and acetic acids are referred to in their anhydrous state; the tartaric and citric in their crystalline. If the latter two acids be pure, a solution of 24.6 grains of the first and of 28 of the last * 1,000 water grain measures of sulphuric acid of specific gravity 1·032, or 32 above water, neutralize 32 grains of soda, and, consequently, one atom, on the hydrogen scale, of each of the other bases, reckoned in grains. Having in the course of many years subjected my tables of sulphuric, nitric, and muriatic acids, as well as of ammonia, to strict cross-examination, I have found them trustworthy for all alkalimetrical and acidimetrical purposes. The bicarbonate must be free from carbonate, a point easily secured by washing its powder with cold water, and drying it in the air. will disengage from 50 grains of bicarbonate of potash 10,000 grain measures of carbonic acid gas. Acidimetrical operations may likewise be performed by determining the weight of carbonic acid gas expelled from the bicarbonate of potash or soda, by a given quantity of any acid, in the apparatus either fig. 7, or fig. 8. Here the weights to be taken are as follows, in reference to Each of these quantities of real acid, with 25 or 26 grains of bicarbonate of potash, will give off 10 grains of carbonic acid gas; and hence whatever weight the apparatus 9 B loses, being reckoned in grains and tenths of a grain, denotes the per-centage of acid in the sample under trial, without the necessity of any arithmetical reduction. Persons accustomed to the French metrical system may use deci-grammes instead of grains, and they will arrive at the same per-centage results. The preceding experiments, in reference to the weight of carbonic acid gas expelled for the purpose c' either alkalimetry or acidimetry, may also be made by means of the ordinary apparatus represented in fig. 9. A is a small matrass which contains the acid or carbonated alkali at its bottom; and conversely the alkali or acid, for their mutual decomposition in the small test-tube, shown first at b nearly upright and filled, but afterward at a, horizontal and emptied. в is a bulbous tube filled with fragments of chlorcalcium for absorbing the aqueous vapor that rises with the carbonic acid gas, and d c is a small bent tube which dips into the liquid in the matrass. The weighings, &c., may be conducted as already detailed; and when the effervescence is completed, the residuary gas is sucked up through B, while the atmospheric air enters to replace it at the orifice d of the bent tube. The NEW Methods which pervade the whole treatise of Drs. Fresenius and Will are all based on the principle of estimating alkalinity, acidity, and the oxygen in manganese (or chlorometry) by the weight of carbonic acid gas evolved. As in taking these measures the gas must be discharged without carrying water off with it, an elegant and ingenious little piece of apparatus has been invented by the authors for effecting that purpose, and it will do it well. A and B (fig. 10) are two flasks (wide-mouthed medicine-bottles may be employed). A must have a capacity of from 2 ounces to 24 B 10 b ounces of water; it is advisable that в should be somewhat smaller, say of a capacity of about 1 to 1 ounces. Both flasks are closed by means of doubly perforated corks. These perforations serve for the reception of the tubes a, c, and d. c is a tube bent twice at right angles, which enters at its one end just into the flask A, but descends at its other end, near to the bottom of B. These tubes are open at both ends when operating; except the top end b of the tube a, which is closed by means of a pellet of wax. The substance to be examined is weighed and put into the flask A, into which water is then poured to the extent of one third of its capacity. B is filled with common English sulphuric acid to about half its capacity. Both flasks are then corked (by which they become united by the rectangular tube), and the apparatus is weighed. The air of the whole apparatus is next rarefied by applying suction to the tube d: the consequence is, that the sulphuric acid contained in в ascends into The expulsion of the gas may be completed by surrounding the flask with a towel dipped in hot water. the tube c, and thus a portion of it flows over into B. Immediately upon its coming into contact with the carbonate contained in A, carbonic acid gas is disengaged, and in its escape must necessarily traverse the oil of vitriol in B, and therein deposite all its aqueous vapor before issuing from d. The sulphuric acid in passing over into a heats the mixture at the same time, and thus promotes the expulsion of the gas. Whenever this ceases to flow, a little more sulphuric acid must be sent over into a by suction from d (or rather from a recurved tube attached, pro tempore, to it); an artifice which may be repeated till no more gas can be expelled, even when the contents of A are heated, as they must be at the end by the excess of oil of vitriol. "From the aperture b of the tube a, which has been all the time closed, the bit of wax is now to be removed, and to the tube connected with d, suction is to be applied, till all the carbonic acid lodged in the apparatus be replaced by atmospheric air. The whole is to be then cooled, wiped, and weighed; the loss of weight indicates exactly the quantity of carbonic acid which existed in the carbonate submitted to experiment. The process is no less neat than it is simple, and does honor to the ingenuity of its inventors. Their mode of deducing the per-centage of alkali from the quantity of carbonic acid discharged in the operation is also quite exact, and suitable for continental chemists familiar with gramme weights and calculations, but certainly not for persons conversant only with ounces, drams, and scruples, or even with grain subdivisions. The whole book, however excellent, needs, for he British public, transposition, before it can serve in this country the purpose intended by its scientific authors. Thus, in section 4, where several results of their analyses are given, the statements have a somewhat mysterious aspect. Should any one ask why the oracular number of 4.83 grammes of carbonate of soda is used as their standard weight for analysis, he can obtain no response in the book, either in a note or anywhere else. A German or French student, familiar with chemical computation, will probably be able to discover that 4.83 grammes of pure carbonate of soda contain, by Berzelius's tables of atomic weights, 2 grammes of carbonic acid; for 53.47 (1 atom of carbonate): 22-15 (1 of carbonic acid): 4.83: 2.00. Such is the simple solution of this apparent enigma, and of some other similar puzzles in the book. Indeed, unless the reader is aware of that proportion, he can not see the grounds of the accordance in the results between experiment and theory, or why the numbers 2.010, 1.993, and 2-020, are presented as specimens of great precision. This accordance gives satisfaction when it is known that these numbers, in experiments 1, 2, and 3, oscillate on one side or other so near to the theoretical number 2.00. But 4 grammes and 83 centi-grammes, as also 1 gramme and 995 milli-grammes, are awkward weights for an ordinary English chemist or apothecary, which would require a month or two's residence in the laboratories of Giessen and Paris to manipulate with readiness. Again, in testing carbonate of potash, our authors take 6.29 grammes as their unity of weight, undoubtedly, because, if pure, it should discharge, by saturation with the sulphuric acid, 2 grammes of carbonic acid. Here, however, they have not stuck so rigidly as the school of Giessen usually does to Berzelius's atomic numbers; for his atom of carbonate of potash is 69-42; whence, 22-15: 69-42 :: 2·00 : 6-68, hydrogen = 1.00; or 276.44 866-33:: 2.00: 6.268 oxygen = 100. Admitting the value of the new method in testing neutral carbonates, it can not be directly applied to the mixed carbonate and bicarbonate of soda, so commonly sold in this country for bicarbonate; nor is it applicable to the case of a mixture of caustic and carbonated alkali, without the tedious process of previous treatment with carbonate of ammonia and heat. The new German method of acidimetry consists in determining how much carbonic acid gas is disengaged from a standard bicarbonate of soda, by a given weight of any acid. The twin-flask apparatus (fig. 10) is used. The weighed portion of acid is put into A, and a sufficient quantity of the soda into a test-tube, which is suspended upright with a silk thread fastened by the pressure of the cork to the mouth of the flask. On letting the thread loose, the test-tube falls, and the cork being instantly replaced, the whole gas evolved is forced to pass through the sulphuric acid in в, and there to deposite its moisture. The experiment is conducted in other respects as already described for alkalimetry. The following extract from Drs. Fresenius and Will's New Methods of Alkalimetry, &c., will show the Giessen plan of calculating results : "The amount of anhydrous acid contained in the hydrated acid under examination is determined from the amount of carbonic acid escaped, as follows: "Two measures of carbonic acid bear the same proportion to one measure of the anhydrous acid in question, as the amount of carbonic acid expelled does to the amount Bought of anhydrous acid. Thus, let us suppose, for instance, we have examined dilute sulphuric acid, and obtained 1.5 grammes of carbonic acid, the arrangement would be: 550 (2 × 275): 501 = 1·5 : x The amount of sulphuric acid operated upon consequently would contain 1:36 grammes of anhydrous acid. Let us suppose the weight of this amount to have been 15 grammes, the sulphuric acid under examination would contain a per-centage amount of 9-06; for 15: 1.36 100: x "SECTION XXIX. Stating the Quantities of the various Acids to be used in their Examination. To enable our readers at once, without the trouble of calculation, to determine from the weight of carbonic acid expelled, the exact amount of anhydrous acid contained in those acids which are of most frequent occurrence, we have subjoined lists of certain quantities to be taken of each acid for experiment, so that the number of centi-grammes of carbonic acid expelled will directly indicate the per-centage amount of anhydrous acid in the acid under examination. "Multiples of those weights may of course be substituted for the numbers given, according to the degree of dilution of the acid under exam.aation. In such cases the number of centi-grammes of the carbonic acid expelled must be divided by the same number, which has served as the multiplier. "These numbers are obtained by dividing the atomic weight of the acid by 550 (2 x 275, one eq. of carbon),t as follows: "Two eq. of carbonic acid, corresponding to one eq. of the acid to be examined, how much should be taken of the latter to expel 100 grammes of carbonic acid? "The arrangement of sulphuric acid, for instance, is as follows:- "When examining acids, it is most advisable to use that multiple of the unity (according to the degree of concentration) which will expel from one to two grammes of carbonic acid. "I. SULPHURIC ACID. "Unity 0-91 grammes (or, more correctly, 0·911 grammes). "Multiples :— “Thus, knowing that 0-91 of anhydrous sulphuric acid will expel 1·00 of carbonie acid, it will be easy to determine what multiple ought to be used, according to the degree of concentration of the acid to be examined." III. CHLOROMETRY, And the testing of Black Oxide of Manganese for its available Oxygen. The value of manganese may be estimated very exactly by measuring the quantity of chlorine which a given weight of it produces with hydrochloric acid; the chlorine being at the same time estimated by the quantity of solution of green sulphate of iron, which it will peroxidize. A process of this kind was long ago practised with chloride of lime (bleaching powder or liquor) by Dr. Dalton; and it has been since improved by Mr. Waltercrum. As the conversion of two atoms of green sulphate of iron into red sulphate requires only one atom of oxygen, this change may be effected by the reaction of one atom of chlorine in liberating one atom of oxygen, while this approariates one of hydrogen from the hydrochloric acid. *New Metho is of Alkalimetry, &c., pp. 93, 94. † A typographical error in Mr. Bullock's edition; it should be carbonic acid. B The weight of 2 atoms of green sulphate of iron is 278 = (139 × 2), consisting of atoms of protoxide = 72, X 2 of sulphuric acid=80, x 14 of water 126; in all=278; and this weight is equivalent to 36 of chlorine, to 8 of oxygen, and to 44 of peroxide of manganese. Therefore, if we take a solution of copperas, containing 278 grains in 1,000 water grain measures, that volume of liquid will represent, by the conversion of its protoxide into peroxide, exactly one atom, either of peroxide of manganese = 44 grains, or 1 atom of chlorine = 36. Hence the following plan of research :Into the flask or phial c of my chlorometric apparatus (fig. 11), put 100 grains of the manganese to be tested, and into the globes A, B, pour out of an alkalimetrical tube charged with 1,000 grain measures of the above equivalent copperas solution, from 200 to 500 grain measures, according to the supposed quality of the manganese; then introduce through the funnel d, some hydrochloric acid of known specific gravity (suppose 1·1), containing nearly 20 per cent. of chlorine, also from a charged alkalimetrical tube, and apply gentle heat to the bottom of the flask by placing it in a capsule of water standing over a spirit-lamp. The chlorine evolved will rise up through the tube f, which passes merely beyond the cork, and will enter into the solution in в and A, converting it into red sulphate. Have ready some dry paper imbued with solution of red ferrocyanide of potassium (red prussiate of iron). Dip a slip of whalebone into the liquor in the globe A, through the funnel e (represented in the figure rather too high above the globe), and touch the paper with its point. As long as it forms a blue spot, some of the iron still exists as black oxide, and the process is to be urged by the addition of a little more hydrochloric acid to the manganese, as long as chlorine gas continues to be disengaged, and while it maintains the level of the liquor in A above that in B. Whenever the liquor, by the reaction of the chlorine, ceases to stain the test-paper blue, more of the solution from the graduated tube must be added till it begins to do so. By the cautious administration of the hydrochloric acid on the one hand, and of the copperas liquor on the other, the term of saturation will be arrived at in a few minutes. The manganese has then produced all the chlorine which it can yield. The number of water grain measures, of the liquor, or degrees of its alkalimeter scale being multiplied by 44, will give a product denoting the per-centage of pure manganese present in the sample; or being multiplied by 36, a product which will denote the quantity of chlorine by weight which 100 grains of it can serve to generate. 11 = Since one atom of pure manganese (44 grains), in producing 36 grains of chlorine, consumes 2 atoms = 74 grains of hydrochloric acid, the quantity of this acid expended from the graduated tubes, beyond the due proportion of chlorine obtained, will show how much of the acid is unprofitably consumed by foreign substances in the manganese. In fact, every grain of chlorine should, with pyrolusite, be generated by an expenditure of little more than 2 grains of real muriatic acid, or 10 grains weight of the dilute acid, : about 9 grain measures of the graduated tube. Liquid hydrochloric acid of spec. grav. 1-093 contains in 1,000 grain measures exactly 200 grains of real acid. Hence 100 grains of pure pyrosulite should produce about 82 grains of chlorine, and consume about 169 of real muriatic acid=845 grain measures of liquid acid, spec. grav. 1.093. Instead of taking 100 grains of manganese as the testing dose, 10 or 20 grains may be taken, according to the dimensions of the apparatus and the exactness of the operator. But if it be wished to obtain direct per-centage of manganese by the graduated tubes without the trouble of reduction, then for a dose of 10 grains take a solution of fresh green copperas (free from adhering moisture), containing 632 grains in 10,000 grain measures. Proceed as above directed. If the manganese be a pure peroxide, 10 grains of it *Berzelius, in the 4th edition of his Lehrbuch, rates the atom of the green sulphate of iron (ferrous sulphate; at 129-43, hydrogen = 1, and considers it, after Mitscherlich, to contain only 6 atoms of water. I have ascertained, by the most careful experiments, that it contains 7 atoms of water; and that 139 grains of it, or 138-44 (Berzelius) are equivalent to 1 atom of chlorbarium, and to very nearly 40 grains of peroxide of iron. This remarkable error has probably arisen from an attempt to measure the proportion of water in the salt from its loss of weight by desiccation. But I have found it impossible by this means to expel more than 6 atoms of water without causing partial decomposition of the salt by disengagement of sulphuric acid. The copperas so dried acquires such an affinity for water, that it absorbs fully one tenth of its weight of moisture from the atmosphere in the course of an hour. |