liberated, and muriate of ammonia is formed. If the gases be perfectly dry, heat is evolved, and a flame is said to traverse the vessel in which the muriate is formed.

Er. 14.-Chloride of sulphur. Heat sulphur in chlorine; it absorbs rather more than twice its weight of the gas, and forms a greenish yellow liquid, consisting of 15 sulphur and 33.5 of chlorine. It exhales suffocating and irritating fumes when exposed to the air. Its specific gravity is 1·6, and dissolves sulphur and phosphorus.

Er. 15.-Chloride of phosphorus, consisting of 11 phosphorus and 33.5 chlorine, is procured by distilling a mixture of phosphorus and corrosive sublimate, or perchloride of mercury. Calomel or the protochloride is left in the retort, and the phosphorus combines with one proportion of chlorine as it passes over.

Er. 16.-Take a jar of chlorine and immerse in it a paper dipped in oil of turpentine, and the gas will inflame the turpentine.

Caution.-Chlorine must be experimented upon with great care, from its pungent odour and suffocating properties; and it is advisable for young beginners not to experiment with such things as oxyde of chlorine, chloride of nitrogen, &c.

CHEMICUS AMATOR.

ANALYSIS OF MINERAL WATERS.
(Resumed from page 168, and concluded.)

3. We have next to ascertain the proportion of mineral acids or alkalis, if any be present uncombined. The acids which may be present, omitting the gaseous, are the sulphuric, muriatic, and the boracic.

The proportion of sulphuric acid is easily determined. Saturate it with barytes water, and ignite the precipitate. 100 grains of sulphate of barytes thus formed indicate 34.0 of real sulphuric acid.

Saturate the muriatic acid with barytes water, and then precipitate the barytes by sulphuric acid. 100 parts of the ignited precipitate are equivalent to 23.73 grains of real muriatic acid.

Precipitate the boracic acid by means of acetate of lead. Decompose the borate of lead by boiling it in sulphuric acid. Evaporate to dryness. Dissolve the boracic acid in alcohol, and evaporate the solution; the acid left behind may be weighed.

To estimate the proportion of alkaline carbonate present in a water containing it, saturate it with sulphuric acid, and note the weight of real acid necessary. Now 100 grains of real sulphuric acid saturate 120.0 potash, and 80.0 soda.

4. The alkaline sulphates may be estimated by precipitating their acid by means of nitrate of barytes, having previously freed the water from all other sulphates; for 14.75 grains of ignited sulphate of barytes indicate 9.0 grains of dried sulphate of soda; while 14.75 sulphate of barytes indicate 11 of dry sulphate of potash.

Sulphate of lime is easily estimated by evaporating the liquid containing it, to a few ounces (having previously saturated the earthy carbonates with nitric acid), and precipitating the sulphate of lime by means of weak alcohol. It may then be dried and weighed.

The quantity of alum may be estimated by precipitating the alumina by carbonate of lime or of magnesia (if no lime be present in the liquid).Eleven grains of the alumina, heated to incandescence, indicate 100 of crystallized alum, or 55 of dried salt.

Sulphate of magnesia may be estimated, provided no other sulphate be present, by precipitating the acid by means of a barytic salt, as 14.75 parts of ignited sulphate of barytes indicate 7.46 of sulphate of magnesia. If sulphate of lime, and no other sulphate, accompany it, this may be decomposed, and the lime precipitated by carbonate of magnesia. The weight of the lime thus obtained, enables us to ascertain the quantity of sulphate of lime contained in the water. The whole of the sulphuric acid is then to be precipitated by barytes. This gives the quantity of sulphuric; and subtracting the portion which belongs to the sulphate of lime, there remains that which was combined with the magnesia, from which the sulphate of magnesia may be estimated.

If sulphate of soda be present, no earthy nitrate or muriate can exist. Therefore, if no other earthy sulphate be present, the magnesia may be precipitated by soda, dried and weighed; 2.46 grains of which indicate 7.46 grains of dried sulphate of magnesia. The same process succeeds when sulphate of lime accompanies these two sulphates ;only in this case the precipitate, which consists both of lime and magnesia, is to be dissolved in sulphuric acid, evaporated to dryness, and treated with twice its weight of cold water, which dissolves the sulphate of magnesia, and leaves the other salt. Let the sulphate of magnesia be evaporated to dryness, exposed to a heat of 400°, and weighed. The same processes succeed, if alum be present instead of sulphate of lime. The precipitate in this case, previously dried, is to be treated with acetic acid, which dissolves the magnesia, and leaves the alumina. The magnesia may be again precipitated, dried, and weighed. If sulphate of iron be present, it may be separated by exposing the water to the air for some days, and mixing with it a portion of alumina.Both the oxide of iron, and the sulphate of alumina, thus formed, precipitate in the state of an insoluble powder. The sulphate of magnesia may then be estimated by the rules above given.

Sulphate of iron may be estimated by precipitating the iron by means of prussic alkali, having previously determined the weight of the precipitate produced by the prussiate in a solution of a given weight of sulphate of iron in water. If muriate of iron be also present, which is a very rare case, it may be separated by evaporating the water to dryness, and treating the residuum with alcohol, which dissolves the muriate, and leaves the sulphate.

5. If muriate of potash or of soda, without any other salt, exist in water, we have only to decompose them by nitrate of silver, and dry the precipitate; for 18.2 of muriate of silver indicate 9.5 of muriate of potash; and 18.2 of muriate of silver indicate 7.5 of common salt.

> The same process is to be followed, if the alkaline carbonates be present; only these carbonates must be previously saturated with sulphuric acid; and we must precipitate the muriatic acid by means of sulphate of silver instead of nitrate. The presence of sulphate of soda does not injure the success of this process.

If muriate of ammonia accompany either of the fixed alkaline sulphates, without the presence of any other salt, decompose the sal ammoniac by barytes water, expel the ammonia by boiling, precipitate by diluted sulphuric acid, and saturate the muriatic acid with soda. The sulphate of barytes thus precipitated, indicates the quantity of muriate of ammonia, 14.75 grains of sulphate indicating 67.0 grains of this salt. If any sulphates be present in

For

the solution, they ought to be previously separated. If common salt be accompanied by muriate of lime, muriate of magnesia, muriate of alumina, or muriate of iron, or by all these together, without any other salt, the earths may be precipitated by barytes water, and redissolved in muriatic acid.They are then to be separated from each other by the rules formerly laid down, and their weight, being determined, indicates the quantity of every particular earthy muriate contained in the water. 50 grains of lime indicate 100 of dried muriate of lime; 30 grains of magnesia indicate 100 of the muriatic of that earth; and 21.8 grains of alumina indicate 100 of the muriate of alumina. The barytes is to be separated from the solution by sulphuric acid, and the muriatic acid expelled by heat, or saturated with soda; the common salt may then be ascertained by evaporation, subtracting in the last case the proportion of common salt indicated by the known quantity of muriatic acid, from which the earths had been separated.

When sulphates and muriates exist together, they ought to be separated either by precipitating the sulphates by means of alcohol, or by evaporating the whole to dryness, and dissolving the earthy muriates in alcohol. The salts thus separated may be estimated by the rules already laid down.

When alkaline and earthy muriates and sulphate of lime occur together, the last is to be decomposed by means of muriate of barytes. The precipitate ascertains the weight of sulphate of lime contained in the water. The estimation is then to be conducted as when nothing but muriates are present, only from the muriate of lime that proportion of muriate must be deducted, which is known to have been formed by adding the muriate of barytes.

When muriates of soda, magnesia, and alumina, are present together with sulphates of lime and magnesia, the water to be examined ought to be divided into two equal portions. To the one portion add carbonate of magnesia, till the whole of the lime and alumina is precipitated. Ascertain the quantity of lime, which gives the proportion of sulphate of lime. Precipitate the sulphuric acid by muriate of barytes. This gives the quantity contained in the sulphate of magnesia and sulphate of lime ;subtracting this last portion, we have the quantity of sulphate of magnesia.

From the second portion of water, precipitate all the magnesia and alumina by means of lime-water. The weight of these earths enables us to ascertain the weight of the muriate of magnesia and of alumina contained in water, subtracting that part of the magnesia which existed in the state of sulphate, as indicated by the examination of the first portion of water. After this estimation, precipitate the sulphuric acid by barytes water, and the lime by carbonic acid. The liquid, evaporated to dryness, leaves the common salt.

6. It now only remains to explain the method of ascertaining the proportion of the nitrates which may exist in waters.

When nitre accompanies sulphates and muriates without any other nitrates, the sulphates are to be decomposed by acetate of silver. The water, after filtration, is to be evaporated to dryness, and the residuum treated with alcohol, which dissolves the acetates, and leaves the nitre, the quantity of which may be easily calculated. If an alkali be present, it ought to be previously saturated with sulphuric or muriatic acid.

If nitre, common salt, nitrate of lime, and mu

riate of lime or magnesia, be present together, the water ought to be evaporated to dryness, and the dry mass treated with alcohol, which takes up the earthy salts. From the residuum, redissolved in water, the nitre may be separated, and calculated as in the last case. The alcoholic solution is to be evaporated to dryness, and the residuum redissolved in water. Let us suppose it to contain muriate of magnesia, nitrate of lime, and muriate of lime.Precipitate the muriatic acid by nitrate of silver, which gives the proportion of muriate of magnesia and of lime. Separate the magnesia by means of carbonate of lime, and note its quantity. This gives the quantity of muriate of magnesia; and subtracting the muriatic acid, contained in that salt, from the whole acid indicated by the precipitate of silver, we have the proportion of muriate of lime. Lastly, saturate the lime added to precipitate the magnesia with nitric acid. Then precipitate the whole of the lime by sulphuric acid; and subtracting from the whole of the sulphate thus formed, that portion formed by the carbonate of lime added, and by the lime contained in the muriate, the residuum gives us the lime contained in the original nitrate; and 35 grains of lime form 100 of dry nitrate of lime.

ENGRAVING.

(Resumed from page 133.)

NEXT to the tools necessary, it is advisable to offer a few remarks upon the materials employed. The chief of these is, of course, the substance to be engraved upon, either copper or steel. Plates of these metals, of various sizes and thicknesses, are prepared ready for the engraver by persons who make it their sole employment; and those who are able to procure them thus prepared, will find it infinitely better to do so than to prepare the plates themselves; but should they live far off in the country, or for other reasons desire to prepare their own copper-plates, (for steel, they will, perhaps, not attempt,) the following observations may guide them :-Let them procure a sheet or piece of thick copper, the thickness (if a small plate) being about equal to that of a thin mill-board, or four cards pasted together. Let them carefully clean and polish both sides with sand, emery and water, or charcoal; wiping this off carefully that no grit may remain, let the plate be passed two or three times through a flatting mill, or wanting this, let it be planished by a tinman, directing him to keep it perfectly flat. When this is done, and the copper thereby hardened, let one surface be rubbed all over with a piece of snake stone; a piece of hone, fine slate, or lithographic stone will do as well. When the plate is thus made smooth, and the inequalities of the hammer are removed, rub it over in the same manner with a piece of fine charcoal and oil; any bark, knot, or grit in the charcoal being first carefully rasped off it. Instead of charcoal fine washed emery may be used. Finally, the plate is smoothed around the edges with a plane or file, and polished with whitening. It will now be fit for use: a great deal of the success of the after operation will, however, depend upon the quality of the copper, as well as the preparation of it. Another method by which a plate may be made at once, is by the electrotype process. A plate, as a pattern, being first procured, another plate may be deposited upon that, which being removed, a second and a third plate in like manner may as easily be made, and if the operation has been well

conducted, all will be of excellent quality, and cost but a trifle; (the whole process of the electrotype will be found in Vol. I;) indeed thousands of plates are now made in London by this process.

The next material is etching ground. The use of it is to lay a ground upon the plate previous to etching it, as afterwards described. It may be bought along with the plates, or it may be made by the following receipt, and which, by experience, we know may be depended upon. The prescribed quantity will make enough to last for a long period, and cover a great number of plates:-Melt together 1 ounce of white wax, 1 ounce of asphaltum, and a quarter of an ounce each of common pitch and Burgundy pitch; let the whole boil ten minutes, then pour it into cold water, and mould it into a ball with the hands; when cold, tie it up in a piece of silk or taffeta.

Bordering wax is a substance used to form a ridge around the plate when it has been etched and is about to be bitten in by the acid. Its only use is to prevent the acid from running off at the edges of the plate; common shoe-makers' wax will do very well; so will glaziers' putty, though the following is most usually employed. As it is not wasted when in use, a stock of half a pound will last for years:-Melt together 2 ounces of rosin, 2 ounces of common pitch, and 4 ounces of yellow bees'-wax; when melted, pour the mixture into cold water, and as soon as it is sufficiently cooled, knead it well with the hands.

Acids required.-It is advisable in procuring a supply of acid for biting in, to choose the strong nitric acid, and not the common aqua fortis; strength for strength, it is but little dearer, and the engraver knowing the article he is operating with to be of first quality, can proceed with greater confidence. It should be diluted only when wanted, and in a degree according to the nature of the subject this practice alone can teach.

The

Brunswick black varnish is purchaseable at most respectable oil shops. Its use to the engraver is to stop out, that is, to cover over false lines, and other defects, previous to biting in; and also during this part of the process, when a portion of the plate is bitten in enough, the rest of it requiring a further action of the acid. To be good, Brunswick black should dry in three or four minutes; it may be made by dissolving asphaltum in spirits of turpentine. If too thick at any time, it is to be diluted with spirits of turpentine. This liquid must therefore be in readiness, not only for the above, but other purposes, afterwards described. The Brunswick black varnish is to be laid on with a camel's-hair pencil. A wax taper is the last material required. intention of it is to smoke the ground of the plates, previous to transferring the picture which is to be etched upon them. The taper adapted to this purpose is that which is white, very long, and about the thickness of a goose quill, sold at oil-shops for 6d. Procure one of these tapers; if the weather be cold, soak it for a few minutes in luke-warm water, draw it out in length, wipe it dry, and fold it up or else cut it into eight equal pieces, which are to be twisted together, forming as it were a candle with eight wicks. A dabber is also wanted; this may very easily be made by the artist, as it consists merely of a handful of wool or cotton wadding, tied up in a piece of silk; some persons put inside and behind the wadding a piece or two of stiff card, cut of a round form, in order to make the dabber keep its shape better, but this is by no means necessary. The

dabber is used in the first process of laying the ground evenly upon the plate to be etched. It is, therefore, indispensable.

An oil rubber is made of a long strip of woollen cloth or flannel with the selvage to it. Take about two yards in length of this list, and roll it up tightly like a ribbon on its roller, so that the selvage shall form an even flat surface. Tie it tightly together and keep it for use; it is valuable in cleaning off a plate, after the scraper, burnisher and charcoal has been used upon it, it is rubbed over the part of the plate requisite, together with a little sweet oil.

The writing engravers, and those who execute mathematical engravings, often require little trifles in addition to the above, but as they are only of partial use, and not even absolutely necessary, we have not thought it requisite to mention them. These are, indeed, all the materials requisite for the most extensive business, costing, with the exception of the copper and steel plates, altogether, both tools and substances, not more than 6s. or 78. The next paper will explain the process of etching.

lb

Note.-Copper and steel plates for engravers, and also etching ground, may be purchased of Mr. Hughes, Shoe Lane. London; or of Mrs. Large, Dean Street, Fetter Lane, London. A plate of copper, the size of the smallest card, costs 34d. Next size card, 7d. A plate about the size of one page of this book may be 3s. or 3s. 6d. The general price is 3s. weight. Steel double the price. A ball of etching ground costs 1s. Engravers' tools may be bought of Mr. Knight, Foster Lane; Mr. Fenn and Mr. Buck, Newgate Street; and Mr. Holtzaffel, Charing Cross. Gravers are from 3d. to 6d. each; handles to ditto. Id. A burnisher, 1s. Scraper, 3s. 6d. Etching needle, 6d. Sand cushions, of various prices-one costing 18. is fit for ordinary occasions.

FLAT IRON WIRE ROPES.

ROUND iron wire ropes have for upwards of two years been successfully used in the collieries on the Continent. Another improvement in these ropes has been made, which will render them still more useful. M. Louis Goens, manufacturer at Termonde, in Belgium, has obtained a patent for flat iron wire ropes. This cordage, which resembles in a great degree flat hempen ropes, possesses extraordinary strength. When properly applied, it will last twice or three times as long as the ropes in present use, and yet the new rope costs a fifth less. Independently of these advantages the flat iron wire cord is more flexible, less bulky, and a great deal lighter than the ropes now used. The latter fact deserves the serious attention of mine proprietors especially, for a great quantity of power is now unprofitably employed in deep shafts in bringing up the weight of the rope alone. The first of these flat iron ropes manufactured by M. Goens, were applied by Messrs. Picard, Davignon, and Co., proprietors of the coal mine of La Bonne Fortune, near Ans, where they are now working, and give great satisfaction. Those gentlemen were the first mine proprietors who employed the round iron wire ropes.

POLARIZATION OF LIGHT.

To the Editor.

SIR. In the interesting article on the polarization of light, recently published in your Magazine, there are two or three observations which have induced me to solicit further information; in doing so, I would remark that it is a subject to which I have given some attention, and that I have had considerable experience in the use of an oxy-hydrogen polariscope. I make these remarks that it may not be supposed that I ask idle questions, or that I seek information to be procured, by reading the ordi