PLATE XI. Account of Dr. Wollaston's Scale of Chemical Equivalents, from Thomson's An. of Philos. vol. 4, p. 176.* of This scale is of so much convenience to the practical chemist, that I seize the earliest opportunity to make it known to my readers in general. It gives the composition of any weight whatever any of the salts contained on the scale, the quantity of any other salt necessary to decompose it, the quantity of new salt that will be formed, and many other similar things, which are perpetually occurring to the practical chemist, and cannot be answered without an arithmetical calculation. I have used such a scale for above six months, and found it attended with numberless advantages. I cannot undertake to explain the instrument, either more clearly, or in fewer words, than Dr. Wollaston himself has done in his own paper. I conceive, therefore, that the best thing I can do is to present my readers with the following extract from that paper, which contains the most material part of it, as far as the explanation of the instrument is concerned: "It is not my design, in the table which follows this paper, to attempt a complete enumeration of all those elements or compounds which I suppose to be well ascertained, but merely to include some of those which most frequently occur. I do not offer it as an attempt to correct the estimates that have been formed by others, but as a method in which their results may be advantageously applied in forming an easy approximation to any object of our inquiries. "The means by which this is effected may be in part understood by inspection of the Plate [II.], in which will be seen the list of substances intended to be estimated, arranged on one or the other side of a scale of numbers in the order of their relative weights, and at such distances from each other, according to their weights, that the series of numbers placed on a sliding scale can at pleasure be moved, so that any number expressing the weight of a compound may be brought to correspond with the place of that compound in the adjacent column. The arrangement is then such, that the weight of any ingredient in its composition, of any re-agent to be employed, or precipitate that might be obtained in its analysis, will be found opposite to the point at which its respective name is placed. "In order to show more clearly the use of this scale, the Plate exhibits two different situations of the slider, in one of which oxy * Dr. Wollaston's paper is published in the Philosophical Transactions for 1814, parti. gen is 10, and the other bodies are in their due proportion to it, so that carbonic acid being 27.54, and lime 35.46, carbonate of lime is placed at 63. "In the second figure, the slider is represented drawn upwards till 100 corresponds to muriate of soda; and accordingly the scale then shows how much of each substance contained in the table is equivalent to 100 of common salt. It shows, with regard to the different views of the analysis of this salt, that it contains 46.6 dry muriatic acid, and 53.4 of soda, or 39.8 sodium, and 13.6 oxygen; or if viewed as chloride of sodium, that it contains 60.2 chlorine, and 39.8 sodium. With respect to re-agents, it may be seen that 285 nitrate of lead, containing 191 of litharge employed to separate the muriatic acid, would yield a precipitate of 237 muriate of lead, and that there would then remain in solution nearly 146 nitrate of soda. It may at the same time be seen, that the acid in this quantity of salt would serve to make 232 corrosive sublimate, containing 185.5 red oxide of mercury, or would make 91.5 muriate of ammonia, composed of 6 muriatic gas (or hydro-muriatic acid), and 29.5 ammonia. The scale shows also, that for the pupose of obtaining the whole of the acid in distillation the quantity of oil of vitriol required is nearly 84, and that the residuum of this distillation would be 122 dry sulphate of soda, from which might be obtained, by crystallization, 277 of Glauber salt, containing 155 water of crystallization. These and many more such answers appear at once by bare inspection, as soon as the weight of any substance intended for examination is made by motion of the slider correctly to correspond with its place in the adjacent column. "With respect to the method of laying down the divisions of this scale, those who are accustomed to the use of other sliding-rules, and are practically acquainted with their properties, will recognise upon the slider itself the common Gunter's line of numbers (as it is termed), and will be satisfied that the results which it gives are the same that would be obtained by arithmetical computation. "Those who are acquainted with the doctrine of ratios, and with the use of logarithms as measures of ratios, will understand the principle on which this scale is founded, and will not need to be told that all the divisions are logometric, and consequently that the mechanical addition and subtraction of ratios here performed by juxta-position, correspond in effect to the multiplication and division of the numbers by which those ratios are expressed in common arithmetical notation. "To others who are not equally conversant with the nature of logarithms, and consequently have not so correct a conception of the magnitude of ratios, some further explanation of the mode in which the scale of equivalents is constructed, will, I presume, be acceptable. They will observe, that the series of natural numbers are not placed at equal intervals on the scale; but that at all equal intervals are found numbers which bear the same proportion to each other. In fig. 3, some of the larger intervals alone are represented on a line similarly divided. The succession of intervals, marked A, B, C, D, E, are all equal, and at these points of division are placed numbers 1, 2, 4, 8, 16, which increase progressively by the same ratio. And since the series 3: 6: 12: 24 increase in the same ratio of 1 to 2, these intervals a, b, c, d, e, are the same as the former. At another succession of different yet equal intervals, marked F, G, H, I, are placed numbers 1, 3, 9, 27, which increase regularly by an equal ratio of 1 to 3; and by means of a pair of compasses it would be found that the interval from 2 to 6, or from 6 to 18 (which are the same ratio of 1 to 3), is exactly equal to F G, the interval between 1 and 3. As any single space represents any one ratio, so the sum of any two or three equal spaces represent a double or triple ratio. If 1 be increased three times by the ratio of 1 to 2, it becomes 8, which bears to 1 triple the ratio of 2 to 1. This ratio is therefore represented by A D, which is the triple of A B. "The distances of the intermediate numbers 5, 7, 10, 11, 13, &c. from 1 are likewise made proportional to the ratios which they bear to 1, and are easily laid down by means of a table of logarithms; for as these are arithmetic measures of the ratios which all numbers bear to unity, the space proportionable to them become linear representations of the same quantities. "As the entire spaces AD, A E, represent the ratios of 8 and of 16 respectively to 1, so the difference D E represents the ratio of 8. and 16, which stand at D and E, to each other. And in the same manner any other space, kl, represents correctly the ratio of 7 to 13; so that the measure of a fraction expressed by quantities that are incommensurate is rendered as obvious to sight as that of any simple multiple. And if a pair of compasses be opened to this interval, and transferred to any other part of the scale, the points of the compasses will be found to rest upon numbers bearing the same proportion to each other as those from which the interval was transferred. "It is exactly in this manner that the various points in the column of equivalents indicate the several quantities sought in any given position of the slider. The relative distances, at which the articles are placed, represent so many different openings of the compasses rendered permanent and presented to view at once. In the table, which I shall place at the end of this communication, the relation of the various substances enumerated to each other is expressed by numbers.* In the engraved scale of equivalents, the ratios of these numbers are represented by logometric intervals at which they are placed, their several positions being determined by those of their respective numbers on the slider, which is logometrically divided. Consequently all the several points in the column of equivalents will indicate numbers in the same due proportions to each other, whatever part of the scale may be presented to them. Those who seek information may obtain it by inspection; those who already *This has reference to the Philosophical Transactions. Dr. Thomson has not introduced the table in his Annals. C. + possess it may be able to correct the positions of some articles by direct comparison with the best analyses upon record, in whatever numbers the results of those analyses may happen to be expressed." A Substitute for Woulfe's or Nooth's Apparatus, by ROBERT HARE, Few subjects have more occupied the attention of chemists, than the means of impregnating fluids with gaseous substances, The contrivances of Woulfe and Nooth, especially the former, have been almost universally used; and have gained for the inventors merited celebrity. Various improvements in Woulfe's bottles have been devised. Still I believe an apparatus replete with similar advantages, but less unwieldy, less liable to fracture; and having fewer junctures to make at each operation, has been a great desideratum with every practical chemist. It has, however, ceased to be so with me, since I contrived the apparatus which I am about to describe. Fig. 1. represents 3 jars placed concentrically within each other, and so proportioned and situated, as to admit two open-necked concentric bell glasses alternatively between them. The neck of the exterior bell glass is introduced into the tubulure of the receiver above, and receives the neck of the interior bell glass. Into this is inserted a trumpet-shaped tube. The two interior jars are furnished with feet F, f. In order to put this apparatus into operation, remove (without taking them apart) the bell glasses, receiver, and tube from the jars. Pour into the latter the fluid, to be imprégnated, till it reaches the height marked by the dots. The funnel mouth, m, of the receiver being provided with a suitable cork soaked in wax, fasten into it firmly the beak of the retort, containing the generating materials. The bell glasses are then to be replaced in the jars, and arranged as in the figure. It must be self-evident that the gas proceeding from the retort, (if the juncture at m be air tight) must press on the fluid in the innermost jar, through the trumpet-shaped tube. If not imbibed with adequate speed, it must soon press on the fluid at a, causing it to subside to the narrow part of the foot f, and thus to expose a much larger, ce. If the absorption be still inadequate, a further subsidence ensue, and the gas escaping round the brim of the interior ass will act on the fluid at b, and enlarge its surface by deng it to the narrow part of the foot F. Should the increased ure and more extended contact thus obtained, be still incomnt to effect a complete absorption, the excess of the gas may e round the brim of the external bell glass into the atmos But so effectual is this process in promoting impregnation, that I have obtained strong muriatic acid in the central jar, without producing any sensible acidity in the outside one. Absorption into the retort or receiver, is prevented by not allowing as much fluid to be above the mouth of the trumpet-shaped tube, as would be competent to fill the cavity between it, and the termination of the open neck of the exterior bell glass at t. As this neck rises about 2 or 3 inches into the receiver, it prevents any foul matter which may condense or boil over, from getting into the jars. If practicable, it would be better that the bell glasses, and tube, and receiver, should be united together while hot, at the glasshouse. If all could not be joined in this way, it would still be advantageous to unite thus the receiver, and the exterior bell glass. The interior bell and tube might then be fastened together, by grinding or luting. As yet I have only used lutings of waxed cloth, or cork. It may be proper to point out, that 3 or more concentric bell glasses, and 4 or more jars, might be used. The union of the bells, receiver, and tube once effected, it is hardly more troublesome to use 3 than 2. When the fluid in the central jar is saturated, this may be emptied and replenished from the middle jar, the latter from the external one. Then supplying the external jar anew, the process may be continued. The other figures are to explain an apparatus on the same principle, constructed of hollow, oblong paralellopipeds, differing in length more than in breadth; so as to allow a serpentine tube to wind into the interior, and deliver gas under a vessel shaped like a T. Fig. 2. represents a vertical section of the whole as when situated for use.* Fig. 3. a vertical section of the lower vessels only. Fig. 4. a vertical section of the covers alone. Fig. 5. a horizontal section, or ground plan of the lower vessels. The upper vessels are so proportioned as to divide the distances between the lower ones equally. It may be well to mention, that this apparatus, from the facility with which it may be cleaned and inspected internally, admits of being made of porcelain or stone ware.t I have had a cylindrical one constructed of the latter material, in which the covers are in one piece, with a tube in the centre for introducing gas. The apparatus may be made more efficacious, by drilling a series of small holes round the brims of the bell glasses or covers, so as to cause the gas, instead of passing round the brims in large bubbles, to divide itself into very small ones. By this means it will be more thoroughly intermingled with fluid. * Excepting, that the covers ought to be so desed, as that their brims may be lower than the bottoms of the interior vessels over which they are placed respectively. This is necessary to prevent the gas from escaping, ere it have access to the surface of the fluid beneath those bottoms. The apparatus may also be made of glass bottles, duly proportioned, and cut (truncated) alternately near the shoulder and near the bottom. |