that the soap may be perfectly dissolved in it. Thus tallow may be boiled for days in a caustic potassa-lye, of spec. grav. 1.25, without saponification; if the lye be stronger a partial saponification takes place, but being insoluble in the fluid, it floats upon the surface in a solid mass; by the gradual addition of water and continued boiling, at a certain point the mass suddenly becomes thick and clammy, and with more water a kind of emulsion is formed (Scifenleim), which continued heating renders perfectly clear and transparent if a sufficient quantity of alkali be present. In this state it may be drawn into long threads, which on cooling either remain transparent, or are more milky and gelatinous. As long as the hot mass suffered to drop from a spatula exhibits a cloudiness, or opalescence, the boiling is continued, or more alkali added. When excess of alkali is present, the cloudiness arises from imperfect saponification, or want of water; the former is shown by dissolving a little in pure water, which becomes perfectly clear when the whole is saponified; if the lye contain lime, the mixture is also clouded, but the addition of carbonated alkali instantly clarifies it.

In order to separate the soap from water, free alkali and oxide of glyceryle, a large quantity of salt is gradually added to the boiling mass, on each addition waiting until it is dissolved; the first addition increases the consistency of the mass, while each successive portion renders it more fluid, till it loses its threading character, and drops from the spatula in short thick lumps. As soon as the congelation is complete, i. e. when gelatinous flocculæ separate from a clear watery liquid, the fire is extinguished, the soap suffered to collect on the surface, and cooled either on the liquid, or ladled out, and suffered to get solid.

In the former case it contains water, free alkali, and other impurities of the lye, and is therefore ill adapted for commerce, although sufficiently good for domestic purposes. As in other chemical operations a precipitate is purified by boiling it in a fluid in which it is insoluble, so soap is purified by a solution of salt rendered alkaline.

The soap of the first boiling is either re-dissolved in weak alkaline lye, and precipitated by salt several times, or it is boiled with an alkaline solution of salt several times, by which means it is rendered much purer. When the saponified fluid is made with potassa, the salt (chloride of sodium) operates in a two-fold manner: it dissolves in the pasty liquid, and decomposes with the potassa salts of the fat acids, forming on the one side chloride of potassium, and on the other soda or soda-soap. That a decomposition takes place is evident from the altered consistency of the fluid mass. Since chloride of potassium has not the property of separating soda-soap, a larger quantity of salt is added. When potassa-lye is employed in soap-making, the first salting requires more than twice the quantity of salt.

In the preparation of potash soaps, a concentrated potassa-lye is employed for separating the soap. Acetate or tartrate of potassa may be employed on a small scale. In the manufacture of soaps,

the saponification of the fats is not completed by the first treatment with weak lyes; and the subsequent repetition of fresh lyes, beside purifying, also renders saponification more perfect.

In saponifying olive and other oils, the mixture often attaches itself to the bottom of the vessel, and is burned; in these cases the alkaline lye is previously mingled with salt, so that the forming soap is obtained in a state of fine division, and yet prevented from forming a perfect solution. For common house use, soap of the first boil is only treated once with salt; that for commercial purposes is suffered to swell up in a weak salt lye, by means of which it takes up fifteen to twenty per cent. water. Grain soap (Kernseife of the Germans) is generally coloured bluish or greenish, from sulphuret of iron, or copper, or from iron or copper-soaps. By cooling these colouring matters collect more or less in certain points, which gives a marbled appearance to the hard soap. Marbling is generally produced by the addition of sulphate of iron or peroxide of iron to the still soft mass.

For white soap, it is rendered fluid by heating it in a saline alkaline lye, and kept in the covered vessel until all the colouring matters have subsided. The more water the soap has taken up in this operation, the more perfect the separation of the impurities, the whiter the soap. Now since this water is not separated, but sold in the soap, it follows that it has much less real value than the grain soap. The white soap contains from forty-five to seventy, marbled soap from twenty-five to thirty-five per cent. water.

The manufacture of soft soap is the simplest of all. The drying oils, either alone or mixed with train oil, tallow and other fats, are kept boiling with dilute potassa-lye until the saponification is com. pleted, i. e. a mass is formed which draws into long transparent threads. Particular care is paid in its preparation to the dilution of the lye, for all soft soaps are insoluble in moderately strong potassalye, and may be precipitated from their solution by the addition of strong lyes. The fluid would therefore appear cloudy, milky, with an excess of strong lye, and by adding water would become pasty or gelatinous. A deficiency of alkali produces an acid oleate of potassa, which attaches itself in thick masses to the bottom of the vessel; but an addition of lye changes it into a neutral salt. Oxide of glyceryle is not separated from soap, although it might be done by the final use of strong alkaline lyes.

The soft soaps of commerce have a greenish or greenish-brown colour; they are transparent in thin laminæ, shining, soft but not fatty to the touch, of a peculiar odour, and have an alkaline reaction. Tallow is often added to them, which disseminates crystalline particles of stearate of potassa, communicating to them a peculiar grained character. Chevreul and Thenard found in commercial soft soap 39.2 to 44 per cent. oleic and margaric acids, 8-8 to 9.5 potassa, and 46.5 to 52 water. They always contain hydrated oxide of glyceryle and delphinate of potassa, derived from train oil, whence their peculiar odour.

When an alkaline soap is mingled with an earthy or metallic salt,

voluminous white or coloured precipitates ensue, in which the alkali is replaced by the earth or metallic oxide. Thus the salts of lime, magnesia, &c. throw down lime, magnesia, &c. soaps. Hence the curdling appearance, when soap is used with hard waters, arises from the union of the lime or magnesia they contain with the fat acids. If carbonate of lime be in the water, it may be thrown down by a little caustic potassa or lime, which will render it softer; if sulphate of lime or a magnesia salt be present, pearlash (ash-lye) will separate the earths.-Ann. der Chem. und Pharm. xxxvii. 249.

Preparation of Ultramarin.

Tirnmon has given a receipt for the preparation of this substance which differs from those generally employed, inasmuch as a small quantity of arsenic is added to the sulphur.

The quantities employed are:

Clay, very finely sifted

Gelatinous alumina, containing anhydrous alumina
Carbonate of soda, crystallized

100

7

1075

221

5

These substances must be mixed together with the greatest care, the pulverized orpiment is shaken into the carbonate of soda fused in its water of crystallization, and when this is partly decomposed the alumina is added: this latter is obtained by precipitating common alum with carbonate of soda, and washing once with river water. The clay and flowers of sulphur are then added, and the whole placed in a covered crucible, which is slowly warmed, in order to drive off the water; as soon as this is effected it is heated red hot. The heat must be so regulated that the mass sinters together without fusing. It is then pulverized, and suspended in river water, and brought upon a filter. If the ingredients have been well mixed the whole mass may be used, but if not there will be several colourless parts; and if the heat has been raised to fusion there will be brown parts, and more especially when the crucible is of a bad kind and easily destroyed. These appearances however are never seen if the operation has been well conducted. The substance on the filter is not edulcorated. The product has now a beautiful delicate green, or even bluish colour. It is then to be heated in a covered dish, and stirred about from time to time. The temperature may be allowed to rise to a low red heat; it may be kept at this temperature for one or two hours.-Compt. Rend., Mai 1842, p. 761.

Dr. Elsner has published an extensive series of experiments which he made to determine what is really the cause of the blue or green colour of ultramarin. It is well known that the natural lapis lazuli, as well as the artificial, evolves sulphuretted hydrogen when treated with hydrochloric acid, and thereby loses its colour. It would appear, therefore, that the sulphur is the cause of the colour, particularly as this body is always found in artificial ultramarin. Elsner made a large number of experiments, passing sulphuretted hydro

gen over alumina, carbonate of soda, silica and alumina, or over a mixture of all these bodies, but in no case could any other colour than yellow or reddish be obtained, if pure materials were employed; on the other hand, if a very minute portion of iron be added, a green, blue or black colour is produced. Elsner then proceeded to another series of experiments. He heated in a furnace mixtures of "ultramarine base" (consisting of silica, alumina and carbonate of soda) with sulphur. It was found that when the ingredients were pure no colour was produced, but only when they contained iron: flowers of sulphur and ordinary alum both contain traces of iron (the iron in Tirnmon's preparation is probably derivable from the latter substance). He therefore concludes from all his experiments, that ultramarin must contain sulphuret of iron and also sulphuret of sodium'; this latter compound appears frequently to be a higher sulphuret, inasmuch as when treated with acid free sulphur is left behind, while sulphuretted hydrogen is evolved. Elsner finds that a greenish ultramarin may be converted, by carefully heating it in an open vessel, into a blue one, and he is inclined to refer the change to the formation of a higher sulphuret, for he has obtained more free sulphur from the blue than from the green varieties.

It is necessary, in examining the composition of an ultramarin, to make two experiments to determine the sulphur; one with nitric acid, by which the whole quantity is obtained; the other with hydrochloric acid, by which the sulphur of the simple sulphurets is found. With lime, strontia and baryta, similar ultramarins may be obtained. Elsner has given the means of several analyses of the blue and green varieties, to which are subjoined the analyses of a natural lapis lazuli, and of an artificial product by Varrentrapp :

Elements of Chemical Analysis, Inorganic and Organic. By EDWARD ANDREW PARNELL, Chemical Assistant in University College, London. 1 vol. 8vo. Taylor and Walton.

IT is difficult to say whether the benefits of a good practical elementary work on chemical analysis are likely to be most felt by the

teacher of the science or the student: the difficulties which beset the path of the learner in this most important branch of chemistry are so numerous, and the calls on the personal attention of the teacher so frequent, as often to lead in a great measure to the neglect of this truly fundamental part of the study, by the diligent and untiring cultivation of which the pupil may alone hope to attain such a proficiency in manipulation and acquaintance with the resources of the science as shall hereafter put him in a state to attempt with success original investigation. If there be any portion of the discipline of the laboratory more fitted than another to rivet upon the mind of the student the conviction of the absolute necessity of the utmost care, circumspection, order and neatness in the general business of chemistry, it is surely an early and familiar acquaintance with the details of mineral analysis in its most perfect forms.

As an adjunct to the exertions of the teacher, but by no means superseding the necessity of oral and practical instruction, the work of Mr. Parnell appears likely to be in the highest degree useful; it will serve to convey to the attentive student a correct notion of the general routine of operations proper to each of the different classes of analytical research, and the principles upon which such modes of proceeding have been devised, besides affording him a fund of practical detail, an easy reference to which will certainly lighten his labours and accelerate his progress.

The best work on analytical chemistry is Heinrich Rose's 'Handbuch' (a translation of one of the earlier editions by Mr. Griffin has appeared in English): but this work is by no means fitted for the student; it is intended more for the proficient than the learner; the various processes and reactions are discussed at a length which would only confuse a beginner, while the author presumes that all the practical manipulations required in analytical chemistry are fully known to the reader. It is in supplying this deficiency that Mr. Parnell's book promises to be of value. He has selected from Rose those portions most likely to be useful to the junior student, and has added a variety of interesting and useful matter not to be found in the great work referred to.

After briefly describing the ordinary manipulations in use and the management of the instruments commonly employed, the author proceeds to point out, by the aid of a comprehensive and wellarranged set of tables, the effects produced under different circumstances by various "reagents" on the oxides and acids which ordinarily come under the notice of the chemist. These tables have been evidently drawn up with great care, and they well deserve it, since it is by the aid of such that the pupil most easily becomes familiar with the practice of testing for acids and bases, the most elementary operations of qualitative analysis. The more difficult part of this subject, the qualitative examination of substances of complicated nature, is then discussed, including the case of silicates which are not attacked by the common acids. Much of the information here given is put into a tabular and exceedingly condensed and convenient form.