brushing or by burnishing. Articles of zinc, copper, brass, and bronze may be directly tinned in this bath, but those of iron and steel must be first tinned in an immersion solution (see I., 2) or else electro-coppered, then scratch. brushed, and finally placed in the tin bath (McMillianCooper, "Electrometallurgy," 1910 Ed., p. 248; Barclay and Hainsworth, "Electroplating," 1912 Ed., p. 331; Watt and Philip, "Electroplating and Electrorefining,' 1911 Ed., p. 344; Langbein-Brannt, "Electrodeposition of Metals," 1909 Ed., p. 439).

The Roseleur electrolyte is the one most generally used for electro-tinning. It is capable of giving the whitest deposit of any of the tinning baths which are in general use. The objections to it are that it must be worked hot, that heavy deposits cannot be obtained except after a period of several hours, and that the anodes do not dissolve normally, which necessitates that a concentrated solution of tin chloride be added to the working solution from time to time.

The Roseleur bath has been modified in concentration by other electroplaters :-Weiss used a solution containing 1 grm. of fused stannous chloride and 5 grms. of sodium pyrophosphate per litre (McMillian-Cooper, "Electrometallurgy," 1910 Ed., p. 249). A solution recommended as giving excellent results is prepared by dissolving 15 grms. of sodium phosphate crystals in 1 litre of water, and adding 7'5 grms. tin chloride. Work at low current density (Metal Industry, 1906, iv., 138). Another solution, said to have been recommended by eminent authorities, contains 37 grms. sodium phosphate crystals and 20 grms. fused tin chloride per litre. The tension required for this electrolyte was given as I to 1.5 volt, when worked hot (Metal Industry, 1907, v., 376).

3. An electrolyte which gives good results when electrolysed at ordinary temperature is prepared by dissolving 15 grms. of ammonium chloride and 30 grms. of fused stannous chloride in a litre of water. Use pure tin anodes, and regulate the current so as to avoid pulverulent deposits (Metal Industry, 1911, ix., 519).

4. An electrolyte which is strongly recommended as giving excellent results is prepared by dissolving 45 grms. of diammonium stannic chloride per litre of water. Electrolyse at tension of about 1.5 volt (Metal Industry, 1907, v., 376).

5. A good lustrous deposit of tin may be produced by using an electrolyte prepared by dissolving 30 to 60 grms. of cream of tartar (potassium hydrogen tartrate) in a litre of water, and adding 7.5 to 15 grms. of tin chloride crystals. Use pure tin anodes, and electrolyse at temperature not less than 70° C. at E.M.F. of 3 to 5 volts. A good lustrous deposit can be obtained in twenty to thirty minutes; scratch-brush with soft steel brush, or polish on a soft buff wheel, using Vienna lime and kerosene. Keep the solution between 5° and 6° B. (Metal Industry, 1908, vi., 162, 227; 1909, vii., 227).

6. A solution which has been used considerably for tinning articles of iron, steel, and brass is prepared by dissolving 60 grms. of caustic soda in about 800 cc. of water, and 22.5 grms. of fused stannous chloride in small amount of water, then pour the tin solution into the caustic solution and dilute to 1 litre. Electrolyse cold, using pure tin anodes, and potential of 1 to 1.5 volt (Bedell's ("Practical Electroplating," 1909 Ed., p. 143). If the solution becomes impoverished in tin it should be revived by adding fused stannous chloride. If solution assumes a milky appearance, add caustic soda until it clears. Keep at about 11° B.

While the work is being plated it takes on a frosty ap. pearance which is usually porous; the work should then be removed from the bath and scratch-brushed. This may have to be repeated several times, if thick deposits are desired. When mechanical plating-barrels are used scratchbrushing will not be necessary, as the rolling and the rubbing of the articles cause them to become burnished. Articles of iron and steel must first be given a slight coating of copper in a copper cyanide electrolyte, preferably hot.

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7. A tin bath which has given satisfaction is prepared by dissolving 12 grms. of metallic tin in hydrochloric acid, evaporating to expel the free acid, then adding to a solution of 25 grms. of potassium hydroxide, and diluting to 1 litre. The addition of stannous chloride must be made from time to time as needed (Barclay and Hainsworth, "Electroplating," 1912 Ed., p. 330).

8. Elsner used an alkaline electrolyte which he recommends as having given satisfaction for electro-tinning iron and steel. It was prepared by adding 25 grms. of tin tetrachloride to 1000 cc. of water and adding sufficient caustic potash to give a clear solution. He used cast tin anodes, and required a potential of 3 to 5 volts (McMillianCooper, "Electrometallurgy," 1910 Ed., p. 248). 9. Hearn prepared an electrolyte which he used for general work by dissolving 21 grms. of tartaric acid and 30 grms. of caustic soda in 1 litre of water, then adding 3 grms. of fused tin bichloride (McMillian Cooper, "Electrometallurgy," 1910 Ed., p. 249).

(To be continued).

THE SCIENTIFIC WEEK. (From Our Paris Correspondent).

THE AROMA OF COFFEE.

The tonic and stimulating properties of coffee have been known for a long time, Learned men attribute all the virtues of this precious produce to caffeine. But M. Gabriel Bertrand, of the Pasteur Institute, after a certain number of researches undertaken in collaboration with M. Weisweiller, has just discovered that an infusion of coffee owes it aroma, not only to caffeine, which has been studied for a long time past, but also to the presence of a volatile alkaloid recognised by chemists as being pyridine, the smell of which, however, in the mass, is disagreeable. It is probable that the infusion of coffee owes a part of its physiological action to pyridine, of which it contains a proportion corresponding to a quarter of a grm. per kilogrm. of coffee.

M. Gabriel Bertrand has observed that by adding caffeine to boiling sugared water, the aroma of coffee is obtained, but if to this decoction some pyridine is added, in proportion equal to that which is normally contained in coffee, the aroma of the coffee immediately becomes much stronger. It would seem then that traces of pyridine increase the aroma of coffee.

a

Different varieties of coffee contain variable proportions of pyridine. The quantity of pyridine contained in a kilogrm. of coffee varies from 200 milligrms. to 250 milligrms.

THE PRESENCE OF BORON IN MILK AND IN EGGS. The researches that Messrs. Gabriel Bertrand and H. Agulhon, of the Pasteur Institute, have already published concerning the presence of boron in the human organism, have demonstrated that, contrary to what had been sustained formerly, not only this metalloid exists in the animal organism as well as in vegetables, but moreover there is every reason to suppose and admit its normal presence in every degree of the zoological scale.

Following on these results, the same authors have come to think that boron may perhaps be a fundamental element of the living cellule, if, like iron and magnesia, it plays an indispensable part in nutrition exchanges. This question has led them to complete their statical researches by the examination of milk and of birds' eggs. The fact is there is some reason to suppose that if boron really possesses a cellulary importance, it must already exist in the first stages of life; that it must consequently exist in milk-that liquid that has to supply in itself alone, for a considerable period, all the alimentary require. ments of the young mammifer. Likewise, boron must also be found in eggs, that is to say in a state of develop. ment, in which it is not necessary to take into considera.

Now, concerning four species of milk (woman's, ass's, goat's, cow's) collected in the presence of the abovenamed authors, into vessels cleaned by them, the immediate research for boron each time gave them distinct results.

They have likewise discovered the presence of boron in birds' eggs. So, they conclude, that in all probability boron is to be classed along with other catalytic elements of the living cell.

THE SUBTERRANEOUS WATERS OF EGYPT.

Dr. Roux, the Director of the Pasteur Institute, has lately communicated to the Academy of Sciences a very interesting work of M. Audebean Bey, concerning the subterraneous waters of Egypt. This study gives a classification of the grounds from the point of view of their permeability.

The Chief Engineer of the Egyptian State Domains explains the differences that are remarked in the perme. ability of the soil in the valley of the Nile, by the deposits of various sorts, due to the divagations of the sinuosities of the branches of the river and of the natural canals during the pleistocene period, and by the changes effected in the dykes and the breaches of the ancient inundation basins in the course of the centuries during which lasted the system of submersion of flooding, &c.

M. Audebean Bey shows that with the works of mechanical draining, which are at present being undertaken in the North of Delta, it will be possible to give to the soil in that region, to-day waste and uncultivated, the fertility it possessed during the Grecian-Roman period, and perhaps even that of the most remote times. He adds also that when the time has arrived, it will be easy to drain and dry the lakes that lie along the Mediterranean coast and to cultivate the vast superficies they occupy. THE PRESENCE OF RARE METALS IN MINERAL WATERS. M. Jacques Bardet has made a whole series of researches concerning the presence of metals in mineral waters. These experiments, made by means of a spectrograph, have led the author to discover in mineral waters the presence of a large number of metallic elements that were entirely unsuspected; amongst others that are very frequent, that of germanium and of gallium, bodies the existence of which had up till now only been remarked in very rare minerals.

MISCELLANEOUS.

American Chemical Society.-Rochester Meeting. The forty-eighth annual meeting of the American Chemical Society will be held in Rochester, New York, September 9th to 14th, inclusive. A meeting of the Council will be held on Monday night, September 8th, at the Hotel Seneca, immediately following a complimentary dinner to be given to the Council at seven o'clock. The programme will open with a general meeting on Tuesday at 10a.m., in the Assembly Hall at Kodak Park. Members should make a special effort to be present at this opening meeting, as it will not only be one of the most interesting meetings of the session, owing to the fact that it will contain the general addresses, but the whole day will be one of special features, inasmuch as the members of the Society are to be the guests of the Eastman Kodak Company at luncheon following the morning meeting, and the afternoon will be spent in visiting their immense plant at Kodak Park. As the Eastman Company is making special efforts to entertain the membership, it is hoped that every member will endeavour to be present at this first session. A smoker will be held at 8.30 p.m., Tuesday, in Masonic Hall. The divisional meetings on Wednesday, all day, and Thursday and Friday mornings, will be held in the Eastman Building, University of Rochester. The President's address will be

Wednesday; and the subscription banquet, Thursday night, at 7 p.m., at Powers Hotel. On Thursday and Friday afternoons, excursions will be open to the following manufacturing plants:-Bausch and Lomb Optical Co., Taylor Instrument Co., Curtice Bros. Co., J. Hungerford Smith Co., Moerlback Brewery, German-American Button Co., Genessee Reduction Co., Municipal Incinerator, Stecker Lithographic Co., and possibly others. The only opportunity to visit the Eastman Kodak Company will be on Tuesday afternoon. There are already signs that the meeting this September will be the largest that the Society has ever held as a separate organisation, and it is probable that from 700 to 1000 chemists will be present. All papers for the meeting must be in the Secretary's hands on or before August 22nd, or in the hands of secretaries of divisions by August 20th, in order to be on the programme; especially the secretary of the Organic Division requests that organic papers be sent direct to him.

In the Branch

Institute of Chemistry.-Pass List: June-July (1913) Examinations. Of thirty-three candidates who presented themselves for the Intermediate Examination, sixteen passed :-R. L. Amoore, R. O. Bishop, A. Dingwall, J. W. Donaldson, B.Sc. (Edin.), J. G. Duncan, Å. Dunsmore, J. S. Frith, Peter Kerr, B.Sc. (Edin.), K. G. Lochhead, J. W. Lorimer, H. V. Parker, B.A. (Cantab.), H. C. Reynard, F. Smith, F. W. Snelgrove, B.Sc. (Lond.), A. R. Steele, and A. F. Weiss, B.Sc. (Lond.). Of forty-five candidates who presented themselves for the Final Examination, twenty-four passed. of Mineral Chemistry :-B. Campbell, B.Sc. (Lond.), J. A. Pickard, B.Sc. (Lond.), A.R.C.S. (Lond.), E. A. Rayner, B.Sc. (Lond.), and E. W. Skelton, B.Sc. (Lond.); in the Branch of Metallurgical Chemistry: R. J. Dunn, B.Sc. (Birm.); in the Branch of Physical Chemistry: (Miss) G. Thompson, B.Sc. (Lond.); in the Branch of Organic Chemistry J. S. Bainbridge, B.Sc. (Leeds), A. L. R. Clarke, B.Sc. (Lond.), A. Cunningham, B. B. Dey, M.Sc. (Calcutta), J. R. Gray, G. N. Grinling, E. S. Hawkins, B.Sc. (Birm.), P. C. R. Kingscott, A.R.C.S. (Lond.), D. E. Sharp, B.Sc. (Aberdeen), T. F. Smeaton, E. W. Smith, B.Sc. (Lond.), and R. Wheatley, B.Sc. (Leeds); in the Branch of the Chemistry of Food and Drugs, and of Water (Miss) D. J. Bartlett, H. B. Brown, D. W. KentJones, B.Sc. (Lond.), H. A. Phillips, H. V. Potter, and S. H. Stroud.

Growth of Sponge in Filtering Beds of Waterworks. An interesting scientific announcement was made recently at a meeting of the Cardiff Waterworks Committee, when the Waterworks Engineer, Mr. C. H. Priestly, said that he, in conjunction with Professor Parker, had succeeded in overcoming the difficulty experienced with regard to the growth of sponge in the pipes in the filtering area at the Llanishen reservoir. The agent employed was a solution of common salt, and so successful had it proved that up to the present week there Priestly added that Professor Parker himself was so imwas no sign of the reappearance of the growth. Mr. pressed with the result of the experiment that he proposed writing a paper on it to the Geological Society, as a record might prove of assistance to other waterworks encountering similar trouble. The Chairman (Ald. C. H. Bird) said it was very satisfactory to learn that this trouble had at length been got over.

NOTES AND QUERIES.

Our Notes and Queries column was opened for the purpose of giving and obtaining information likely to be of use to our readers generally. We cannot undertake to let this column be the means of transmitting merely private information, or such trade notices as should legitimately come in the advertisement columns.

New Copper Alloy -We notice in CHEMICAL NEWS, vol. cvii., p. 283, an extract relating to a new copper alloy. Can you inform us cobalt-tin alloy? We desire to make some tests with this acid rehow we can obtain samples containing varying proportions of the sisting metal.-1. and W. KEARNS.