March i6, 181,9] 



jVA rURE 



461 



LETTERS TO THE EDHOR. 

 [The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.^ 



On the Colour of Sea Water. 



AlTKEN [Proc. F. S. E., vol. ii. p. 472, 1S82) has given a 

 ;ompIete theory of the colour of sea water as observed at 

 rarious places, based upon the principle that sea water is a 

 jlue liquid. According to this view, the green tint often 

 >bserved in sea water, especially near land, is to be explained by 

 ;he presence of fine yellow particles. During a recent voyage 

 ay the Messageries steamer Polynesien, I was permitted, through 

 :he kindness of Commandant BuUard, to erect a tube 736 cm. 

 ,ong against the rail of the after-deck, and to pass through it a 

 :ontinu^)us stream of water from the ship's salt water service, 

 rhe water was taken in well forward and at a depth of two or 

 :hree metres, and consequently was not soiled by the passage of 

 he ship. I made a series of observations with the apparatus 

 lescribcil, matching the colour of the sea water by making 

 Tii.xtures of definite substances, and using these mi.\tures to fill a 

 ;ube iS cm. long, placed alongside the water tube. Both tubes 

 ivere illuminated by diflused daylight reflected from a white 

 screen, and by the aid of diaphragms, t\:c., it was arranged so 

 ;hat the angular area of the visible part of the screen was the 

 iame whether observed through one tube or the other. Observ- 

 itions were made every day on the voyage from Sydney to 

 Marseilles ; but, owing to the uncertainty arising from the 

 ;ontamination of the water by the varnish with which the 

 nterior of the tube was protected, it is usele.=s to comment on 

 nost of the results obtained, except in so far as they give a 

 neans of easily reproducing the exact lint of pure sea water 

 IS seen through a column 736 cm. long. Make up the following 

 olution : — 



Water, 500 c.c. 



Soluble Prussian blue, 'OOi gram. 



Saturated lime-water just precipitated by the smallest 



excess of bicarbonate of soda, 5 c.c. 



This mixture, when viewed through a tube 18 cm. long, will 



ihow with considerable precision the colour of a sample of 



vater from the Mediterranean, lat. 36° 24' N. , long. 17^ 51' E. 



)f Paris. 



By using various lengths of tubes I found that when a match 

 las once been made, it can be preserved (within the limits 

 ested) by increasing the amount of prussian blue proportionally 



the length of the column of water under investigation. In 

 hese tests I made use of tubes 1S3 cm. long, which could be 

 nounted in series ; the relation held as the number of tubes 

 vas increased from two to five. 



I consider that it would be worth while for a series of measure- 

 nents '.o be made systematically by this method, and therefore 

 nention that the tubes must be of black porcelain or glass ; the 

 vater must be pumped by the observer's private pump(whichmust 

 3e worked off the electric service), and must give a'pressure large 

 mough for a Berkefeld filter. The colour of daylight is also too 

 variable on the deck of a ship protected by awnings, and a form 

 )f artificial illumination should be employed. In making the 

 :olour matches, it is best to arrange to look down the two tubes 

 limultaneously, using one eye for each tube. By slight squint- 

 ng, it is easy to get the sensation of two patches of colour on the 

 icreen seen side by side. 



The majority of the samples of water examined by me took 25 

 per cent, less blue to match them than the example 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 rising to 



1 large proportion of the prussian blue, and, of course, giving a 

 ;reen solution. The transparency of the water is estimated by 

 he amount of precipitated chalk it is necessary to add. At the 

 ame time, I am not sure that the loss of light observed, and re- 

 [uiring this addition to the match, is produced by turbidity. It 

 s just as likely that the absorption spectrum of water is crossed 

 )y a faint but uniform band from end to end. In this case a 

 )lack liquid might be added to make the match, but I do not 

 enow of one which is anything like black in very dilute 

 olution ; of definite materials the best was the aniline dye sold 

 mder the name of steel-grey, but it was very distinctly purple. 



The water on the west and south-west coast of Western Aus- 



:,-o. 1533, VOL. 59] 



tralia 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, 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. 



Richard Threlfai.l. 



45 Frederick Road, Edgbaston, March 4. 



Another Stockton Dragon. 



Since we chronicled in Nature in September last the find of 

 an Ichthyosaurus in Mr. Lakin's pit at Stockton, the men in the 

 neighbouring quarries have thirsted for the renown which a 

 similar discovery would bring. Great care has been employed 

 with the pick as each succeeding layer of clay was reached, and 

 more than one false alarm has been raised. Last week a speci- 

 men less complete, but still remarkable, was unearthed in the 

 cement works belonging to Messrs. Kay and Co. It lies 50 



feet below the surface. The head is tolerably perfect, showing 

 the teeth and one of the eyes. The ribs and paddles ate much 

 dislocated, and the lower part of the tail is wanting. The length 

 of the head is 2 feet 8 inches, of the whole fragment 7 feet. It 

 has been admirably photographed by Mr. Elkington, of Bradwell, 

 Rugby, to whom we were indebted for the first monster, and 

 who will supply copies to geologists and others requiring them. 

 It is hoped that the fossil may be secured for the Warwick 

 Museum. W • T. 



Chemists and Chemical Industries. 



Apart from any question of good taste, it was surely quite 

 unnecessary for Dr. Armstrong to import personal matters into 

 the discussion in which he takes part in his letter appearing in 

 your issue of the 9th inst. 



The causes of the relative positions of this country and Ger- 

 many as regards chemical manufactures, whether due to the 

 real or supposed laches of particular manufacturers or not, are 

 due to national not individual failings, and were admitted so 

 many years back that they have little interest to-day. More- 

 over, they were not under discussion. 



The question was — Whether the best means were being taken 

 to remedy admitted defects in view of the fact that our most 

 successful rivals were demanding what they believe to he 

 improvements in their own methods of producing industrial 

 chemists. , 



With these words, I will leave my friend Dr. Armstrong s 

 version of " Who drives fat oxen should himself be fat," and 

 pass back to ouf subject. 



I gather, then, that the real cause of the alarm in Germany 



