320 Intelligence and Miscellaneous Articles. 



insoluble state some iron, indium, &c. The alkaline liquor, treated 

 with hydrosulphuric gas, then slightly acidulated with sulphuric acid, 

 gives a precipitate consisting principally of sulphide of indium*. 



10. The very slightly acid liquid being boiled with a large quan- 

 tity of water, the gallium passes again into the state of a subsalt. 



11. The gallium is isolated by electrolysis of the potassic solu- 

 tion of the subsalt. The deposition of the metal is effected advan- 

 tageously only under special conditions. The intensity of the 

 electric current, for example, should vary according to the state of 

 the liquor ; but the surface of the negative electrode must always 

 be relatively small compared with that of the positive electrode. 

 In one of our operations, which produced 8 grams of gallium in 

 twenty-four hours, 40 Bunsen elements (18 centims. in height) 

 arranged in eight parallel series, each comprising 5 elements in 

 tension, put in action a negative electrode the double surface of 

 which did not exceed 15 square centimetres, while the positive 

 electrode presented an expanse of about 450 centimetres square. 



The metal, when deposited cold, often forms long files of crystals 

 resembling needles, normally fixed to the electrode by one ex- 

 tremity ; some of them attained the length of 3 centims. Above 30° 

 the metal trickles in drops, which collect at the foot of the electrode. 



By operating in the manner above described, we collected 62 grams 

 of crude gallium. If account be taken of the inevitable losses, and 

 of some grams of gallium which still remain in our various pro- 

 ducts, the content of the Bensberg blende may be estimated at g-oi o"0> 

 or nearly 16 milligrams per kilogram. This minute proportion of 

 material capable of extraction accounts for the operations requiring 

 so long a time. 



We purified the crude gallium by filtering it through linen of a 

 close texture, agitating it in hot water acidified by hydrochloric 

 acid, and repeatedly crystallizing it. From this we afterwards 

 prepared the crystals, plates, and superfused mass of gallium which 

 we have the honour of presenting to the Academy. The little bar 

 was cast with metal not refined. 



In an early communication we will recount various observations 

 made in the course of our operations. — Comptes Rendus de V Aca- 

 demic des Sciences, Feb. 18, 1878, tome lxxxvi. pp. 475-478. 



ON THE RESISTANCE OF FLUIDS. 

 To the Editors of the Philosophical Magazine and Journal, 

 Gentlemen, Berlin, S. W. Grossbeerenstr. 24, March 3, 1878. 



In your Magazine for December 1876, pages 434 and 435, Lord 

 Bayleigh gives two formulae (3 and 4) for the resistance of an 

 elongated blade held vertically in a horizontal stream. These formulae 

 were given before Lord Bayleigh by myself, in a paper entitled 

 "M. Thiesen, zur Theorie der Windstarke-Taf el, Sanct Petersburg, 

 1875," "Wild's Rep.f. Meteorologie, J. iv. No. 9, p. 7. 

 I am, Gentlemen, yours faithfully, 



Dr. M. Thiesen. 



* It must be remarked that indium is but partially precipitated by potass 

 arid by sulphide of potassium. 



