trial centres between New York and Kansas and Chicago and Quebec. The Industrial League entertains high hopes that as a result of the visit, and the establishment of more intimate relations with American manufacturers and employers, a great step forward will be accomplished towards the revival of trade.

TENDERS INVITED FOR AUSTRALIA.-H. M. Senior Trade Commissioner in Australia has forwarded copies of specifications, conditions, and forms of tender in connection with calls for tenders by the Postmaster-General's Department for the supply and delivery of (1) ironwork, including couplings, piping, bolts, rings, &c. (Schedule No. 704); (2) 29,500 porous cells, No. I size to specification (Schedule No. 1685); (3) 20 tons ammonium chloride (Schedule No, 1683). Sealed tenders on the proper forms will be received by the Deputy Postmaster-General, Perth, Western Australia, up to May 25 in the case of (1), and by the Deputy Postmaster-General, Melbourne, Victoria, up to May 31 in the case of (2) and (3). Local representation is essential, and as the time for the receipt of tenders is limited, it will be necessary for firms tendering to instruct their local agents by cable. Copies of the specifications in connection with the above tenders may be consulted by British firms interested at the Department of Overseas Trade (Room 59), 35, Old Queen Street, Westminster, S. W. 1.

THE CASTING OF METALS.-Prof. T. Turner, M.Sc., A.R.S.N.I., of Birmingham University, will deliver the Eleventh Annual Lecture at the Institute of Metals on this subject on Wednesday, May 4, at 8 p.m. The meeting will be at the Rooms of the Institution of Mechanical Engineers, Storey's Gate, Westminster, S. W. 1. Coffee and light refreshments will be provided at the conclusion of the lecture.

REVIVAL IN MANUFACTURE OF LINOLEUM.—The actual penury of linseed oil, colophony, Kauri gum, jute, and cork, as also their high prices, constitute an obstacle to revival of the linoleum industry. By utilising all the accumulated waste, German works were able to resume manufacture, but this resource will only provide for a brief period, the quantity of waste materials being insignificant. Moreover, these works are equipped for a somewhat great production, and all reduction necessarily involves a loss in working. Linseed oil is the most important raw material, but considering its cost other oils are sought after. Whale and shark oil, prices of which are moderate, can, by direct oxidation, be made suitable for linoleum, combined with linseed oil and small quantities of wood oil. By insufflattion of air, as in methods for rapid oxidation, these oils lose their bad odour. By subsequent fusion with colophony, the odour completely disappears, so that the finished products are quite free from a fish oil odour. These oils can also be polymerised in presence of free fatty acids and magnesia; then converted into linoleum, compounds yielding oxygen being added. Other oils may also be employed, viz., perilla oil, soja, grape pips, hemp, walnut, poppy, and sunflower oils, &c. As a substitute for linoxin the pitch of stearin works can be utilised, or colophony can be replaced by rubber resins. These last have the advantage of not forming combinations with zinc, oxide, magnesia.

or lime, differently to colophony, which forms very hard products with them, which make linoleum brittle. To avoid these inconveniences, when these polymerised oils are employed with magnesia, it is well to previously etherise the colophony with glycerin. Hardening is less to be feared with demi-siccative oils. Cork can be replaced by peat or sawdust, and jute by paper tissues.-Chimie et Industrie, January, 1921.

VARIATION IN THE ROTARY POWER OF TARTARIC ACID. Continuing the study of this variation, which is different to that previously given, MR. de Mallemant examines the action of solutions of metallic chlorides and nitrates. The fall increases in the series of alkaline metals and decreases in the order Sr, Ba, Mg, Zn.-Comptes Rendus, January 17, 1921.

Lead Sulphate.-Mr. P. A. Mackay of 70, Lombard Street London, has been granted a Patent No. 157554 for an improved process of obtaining lead sulphate by treating the sulphide ores free from zinc, preferably galena and oleum, which may be in excess without any external heating. The reaction vessel should be insulated to avoid loss of heat. When an excess of oleum is employed, the sulphate is precipitated by dilution with water, and the excess acid may be recovered.

Messrs. Rayner & Co., will obtain printed copies of the published specifications and will forward on post free for the official price of 1/- each.

NEWS

THE CHEMICAL NEWS.

VOL. CXXII, No. 3186.

THE COLOUR AND MOLECULAR FORMULA OF WATER AND ICE. By E. TOMKINSON.

Part 1.

IN connection with Prof. W. D. Bancroft's recent paper on this subject, the following notes may be of interest (sce CHEMICAL NEWS, 1919, cxviii., 197, 208, 222, 233, 248, 254; and 1921, cxxii., 9, 34). (Note.-Rayleigh's work on He and Ar is noticed in the CHEMICAL NEWS, 1920, cxxi., 248, c.f. Nature, 1920, p. 584).

Prof. W. Spring, at the 5th International Congress of Hydrology, Climatology, and Medical Geology, Liège, October, 1898, delivered an address on the colours of natural waters, in which he states that, when pure water has a very slight cloudiness, due to the presence of finely-divided nearly white or colourless particles. Even if these are absolutely colourless, as in the case of very finely-divided rock crystal, a yellow tint is given to the water, which, together with the natural blue proper to the water itself, produces a green colour, as in the cases of the Lakes of Neuchatel and of Constance (c.f. other explanations, Bancroft, loc. cit.). The usually green colour of certain lakes occasionally becomes absolutely colourless, which is due to the washing into the lakes of a fine mud of a reddish tint (iron oxide), which neutralises the green colour, rendering it for the time being perfectly colourless.

The

A rather different aspect of the question was brought forward by the work of Threlfall (Richard Threlfall, Nature, 1899, lix., 461), thus : “During a recent Voyage by the Messageries steamer "Polynesien," I was permitted, through the kindness of Commandant Bullard, to erect a tube 736 cm, long against the rail of the afterdeck, and to pass through it a continuous stream of water from the ship's salt-water service. water was taken in well forward, and at a depth of two or three metres, and consequently was not soiled by the passage of the ship. I made a series of observations with the apparatus described, matching the colour of the sea-water by making mixtures of definite substances and using these mixtures to fill a tube 18 cm. long, placed alongside the water tube.

"Both tubes were illuminated by diffused daylight reflected from a white screen, and by the aid of diaphragms, etc., it was arranged so that the angular area of the visible part of the screen was the same whether observed through one tube or the other. Observations were made every day on the voyage from Sydney to Marseilles, but owing to the uncertainty arising from the contamination of the water by the varnish with which the interior of the tube was protected, it is useless to comment on most of the results obtained, except in so far as they give a means of easily reproducing the exact tint of pure sea-water as seen through a column 736 cm. long.

"Make up the following solution: water 500 cc., soluble Prussian blue, o'001 grm., saturated limewater, just precipitated by the smallest excess of

bicarbonate of soda, 5 cc. This mixture when when viewed through a tube 18 cm. long, will show with considerable precision the colour of a sample of water from the Mediterranean, lat. 36 deg 24min. N., long. 17 deg. 51 min. E. (of Paris). By using various lengths of tubes I found that when a match has once been made, it can be preserved (within the limits tested) by increasing the amount of Prussian blue proportionally to the length of the column of water under consideration.

"In these tests I made use of tubes 183 cm, long, which could be mounted in series; the relation held as the number of tubes was increased from two to five. I consider that it would be worth while for a series of measurements to be made systematically by this method, and therefore mention that the tubes must be of black porcelain or glass; the water must be pumped by the observer's private pump (which must be worked off the electric service), and must give a pressure large enough for a Berkefield filter. The colour of daylight is also too variable on the deck of a ship protected by awnings, and a form of artificial illumination should be employed.

"In making the colour matches, it is best to arrange to look down the two tubes simultaneously, using one eye for each tube. By slight squinting, it is easy to get the sensation of two patches of colour on the screen side by side.

"The majority of the samples of water examined by me took 25 per cent less blue to match them than the sample quoted, and when the water was soiled by the tube, and perhaps at other times, it was necessary to add an amount of picric acid to a large proportion of the Prussian blue, and of course, giving a green solution. The transparency of the water is estimated by the amount of precipitated chalk it is necessary to add. At the same time, I am not sure that the loss of light observed, and requiring the addition to the match, is produced by turbidity. It is just as likely that the absorption spectrum of water is crossed by a faint but uniform band from end to end. In this case, a black liquid might be added to make the match, but I do not know of one which is anything like black in very dilute solution; of definite materials the best was the aniline dye sold under the name of steel-grey, but it was very distinctly purple.

"The water on the West and South-West coast of Western Australia is perhaps more interesting than any I have seen, for it is very green indeed, and very clear; so much so as to raise a doubt of the adequacy of Aitken's explanation (Proc. Roy. Soc. Edin., 1882, ii., 472; see also Bancroft, loc. cit.), especially as the sand looks white rather than yellow. It is just possible that the sea may in certain places dissolve a sufficiency of yellow colouring matter from living or dead sea-weed to account for the green tint. All the observations I made convinced me that the possible scattering of light by very fine particles in suspension has got nothing to do with the colour of the sea-water."

In reply to the above (Nature, 1899, lix., 509), Aitken points out that he never stated that the yellow particles are the exclusive cause of the greenness in sea-waters, and concludes (p. 510): "As the waters of most of our rivers are yellowish brown, it is probable that it is the addition of this yellowish water to sea-water that makes the seas

In Threlfall's paper, reference is made to the absorption spectrum of water. Hartley and Huntington (Phil. Trans., 1879, clxx., 257), using the spark spectrum of an alloy of tin, lead, cadmium, and bismuth, found that water is quite diactinic transmitting all the rays as far as A = 2000 Å. U. On the other hand, Colley (A. R. Colley, Journ. Russ, Phys. Chem. Soc., xxxviii., 431; xxxix., 210) found that absorption bands occur in the optical and electrical spectra of water.

Water vapour, however, shows absorption in the infra-red; for example, the "a" 7165 absorption band, no bands occur for wave lengths of less than A 5884 Å.U. It was by the "a" band that the presence of water-vapour was detected on Mars (see Rolston, Nature, 1997, Ixxvii., 442; Slipher, ibid., 497; Lowell, ibid., 503, 606; Campbell, ibid., lxxxiv., 317).

A dark line or band in the spectrum of water has been reported (T. W. Backhouse, Nature, 1910, lxxxiv., 530) at λ=6000 Å. U. approximately, occurring in buish-green fresh water and in seawater. This line would tend to make water blue, but its effect is masked by strong general absorption in the whole of the red and orange beyond this dark line. In sea-water, this general absorption was found to extend more feebly to the D line of the solar spectrum, and even to the dry air band. The deep green of Lago Maggiore gave an almost identical line. This line was not found in the water of Lake Geneva, noted for its deep blueness, but the general absorption at the red end of the spectrum was very striking Backhouse states that the bluest water is at Lago di Gonda, and the Blane See, near Handersteg. At the former place, the blue colour of the water was slightly tinged with green, but was often bluer than the bluest sky.

Sir E. Ray Lankester (Nature, 1910, lxxxiii., 68) drew attention to the beautiful light-blue colour of the water in storage tanks which had been treated for hardness by Clark's process, the colour being independent of the condition of the sky, and visible at (almost) any angle of vision. He also noticed that the white porcelain of a bath appeared distinctly blue with a layer of water 20in. high in strong sunlight, the intensity of colour varying with the movement of the water in waves or ripples.

It has been shown (H. T. Barnes, Nature, 1910, lxxxiii., 188) that the rich blue colour of the hard clear ice at Glacier, B.C. persists even with small pieces of the ice; and surface ice, which has been slowly formed by conduction, and taken out of the St. Lawrence River, shows the same effectbut the block loses its colour after long exposure to light, and very rapidly in sunlight. Coloured sediment and air-cavities detract from the colour. Barnes attributed this colour to a "real absorption effect due to the large molecular aggregates, which absorb the long rays, and not a "blue-sky" effect. Sea-water is particularly blue, and here we have the added effect of salt molecules (in addition to which the water of the sea is very clear). W. H. Skerzer (Smithsonian Report, 1907) showed that the blue colour of the water and ice of the Canadian Rockies is a real absorption

sence of minute white sediment but not by coloured sediment." He refers to the analogy of the beautiful blue colour of liquid air as soon as most of the nitrogen has boiled away (due to the formation of complex oxygen molecules), and notes that the variations of specific heat, density, viscosity, and compressibility of water_with_temperature are due to gradual diminution of the molecular aggregates. It will be noted that this suggestion is in agreement with that advanced by J., Duclaux and Mme. E. Wollmann (Journ. Physique, 1912, (v), ii., 263—see CHEMICAL NEWS, 1921, cxxii., 9, 34).

W. N. Hartley (Nature, 1910, lxxxiii., 487) found that optically pure water cannot be prepared by distillation, even by first distilling with acid permanganate, and then re-distilling from a copper vessel into a receiver placed in a hydrogen atmosphere (which latter provides an optically pure atmosphere), but pure (optically) water was prepared by Tyndall by melting clear block ice in a vacuum, and this water was blue when viewed through a tube 3ft. in length. Prof. Hartley stated that it is only possible to observe the beautiful blue colour of the water at Fairy Loch beside Loch Lomond, being where it wells up from a fissure in the rock and passes over a vein of milk-white quartzite. In another instance, the blue colour was only observed when a white object was placed in the water. Hartley's explanation is that the blue is wholly due to absorption of rays of complementary colour; because, if not, the reflection of the blue rays by suspended fine particles should be seen against a dark ground on looking into the water, but this was found not to be the case. Against this we know that the light escaping reflection has a reddish-golden colour. He concludes: "In a hazy atmosphere when the sun is low and we look towards it we seen the golden colour; in the opposite direction we see the blue opalescence. The white light from the sky traversed the (last-mentioned) water in two directions to the bottom, and then, by reflection, back again, and it is safe to say that these two opposite colours would neutralise each other." (The water when undisturbed on the surface was almost invisible, but the bottom of the pool was composed of red stone.-E.T.).

A very interesting account of observations made on the "Challenger" and at other times is given by J. Y. Buchanan (Nature, 1910, lxxxiv., 87). He states that the green colour of the Antarctic water is due to the abundance of diatoms, and to a greater extent, to the excretions of animals for the subsistence of which the diatoms furnish the ultimate food supply. He says that the three colours of the ocean are ultramarine and indigo and the above green, and very properly notes that for the correct observation of the colour the greatest amount of light must reach the eye after passing through the water, and the least after reflection. By observation through the "screw-well” of the "Challenger," he was convinced that the water contained in its own mass sufficient colour to account for all that was perceived. As a result of experiments in the mid-Pacific, he concluded that the length of the uninterrupted column of (sea) water which transmits the more colour (pure but pale ultramarine) must be many times greater than 25 fathoms. He showed that the green colour of the sea-water at Mogador is

intense