M E T A L S. 



75 



are red, by reflected light they are grey. Selenium 

 may be made to as-ume the crystalline state, though 

 via difficulty. When slowly deposited from a solu- 

 tion of some of its salts, it puts on the dendritic form, 

 the crystals of which appear, by the aid of a glass. 



i A *- . ,n f ri"."f--i I IV ll\r*IM'.ie. 



tO DC DrWaTM wCVnUHMOTB WJ WeTt^Baaalaafc 



When selenium is heated in close vessels, it boils, 

 ad paaaea of ia vapour, efa colour rather darker than 

 that of chlorine, and which condenses ia the cool part 

 of the apparatus in black drops. 



When heated in the air, or in very huge vililll, a 

 red-coloured veaoer is farmed, which condenses in 

 mutafiiff* When the Mtatl is iMttttcl in i^nrt^**t with 

 bsjaTtbe atoao acquires at its edges a bine eoloar, and 

 the selenium is volatilized with the odour of bone. 



are selenic acid, 

 ixygen, similar to 

 i therefore called it sele. 



the seenum t voatze wt t 

 raddUh. The product* in this CO 

 ami a compound of selenium and 

 carbonic wide. Benetsus kee (be 



the 



It may like, 

 in a large weasel 

 ilr aasjajasjasj t 



sparingly soluble in water, but comeaaaicates to that 

 aid its peculiar odour. It dues act seem to 

 with the alkalies. 



Selenium combines with a I 



of acsd properties. Wbea a stream of osygea ia _ 

 over selenium in a elate of fission, the raetoJ take* ire. 

 i with a white flaeae, having a 



the oool part of the i 

 ealy pnred by 



. * . __ 



i i - *- _ ;.,!. , i i. . 



11 fMll . ' -li. J- 1 l i M |> X I i ."I 1 .( . 1 . , A , . ,. . ;;; 



the furm of a white mate. When UM. M ubiaeted to a 



hoi. and yields on disullation with this laid, a Uaead 

 havutgaaetherialcdoar; at the same tiaae a 

 of selenium ie (armed, and put of the acid 



HBaaL 



FIjmliaM ndcvTovrvd to Mc.trtaain the 

 of thiaaeid, by ps.ag ehWioe over the metel. la 

 !, 1 of seteBiesa united with 1.79 of 

 According to Btritlsaa, 1.79 of 

 are equivalent to 4*043 of oxygen 100 of . 

 tiasafcn, aasto with 4O.43 of oxygen, to form 



oxygen. According to this experiment, 100 of sele- 

 nium combine with 4". J?i oxygen. 



Berzelius is inclined to consider, that the true com- 

 positioo of the acid is 



100 selenium, 71.26, 



40.33 oxygen, 28.74 ; 



and that it contain! 1 atom of selenium, and 2 of oxy- 

 gen. If so, the number for selenium is 4.959, that of 

 oxygen being 1. 



Thomson, from calculation founded on the for- 

 mer of thaw experiments, infers that the acid is com- 

 posed of 



100 selenium , 



98 oxygen. 



The cause of this diaerence is owing to a difference 

 entertained with respect to the constitution of the pre- 

 cipitate, afforded by the nitrate of silver. According 

 to Dr. Thomson, the equivalent number for selenium is 

 5.185, that for the acid 7 



CfUorieV of Selauxm. When selenium is kept in 

 chlorine, the gas is absorbed, the metal becomes hot, 



end a bnwa ouleuied liquid ia formed, which assumes 

 a white colour M the absorption of the gas proceeds. 

 According to Bendies, the product of this experiment 

 ia selea*e and muriatic acids. According to Sir H. 

 * doctrine, k ia a chloride. When dissolved in 

 water, it form, a transparent colourless add solution. 



When Ibis coaaaoand is heated in contact with se> 

 laaiens. a yellowish fluid is formed, which, when put 

 into water, decomposes it, and generates muriatic and 

 selenic adds, and deposits selenium, It is probable 

 that this u another naasaaiiaJ of selenium and chlo- 

 rine, containing leas chlorine. If so, it is the pro- 

 torhssside, and the former is the perchloride of the 

 total 



StltmiurttlfJ HyJragtn. Selenium combines with 

 * forms a gasioai fluid, called aeleniurrt- 

 whicb is piucsaad by adding muriatic 

 seleniuret of potassa. It 

 ia absorbed by water, farming a transparent colourless 

 solution, having a hepatic taste, and which *tains the 

 .km red. and reddens litmus. The solution, after be- 

 ing kept for some time, bicoam turbid, from the de- 

 position of selenium. When exposed to the air, the 

 niaaiersttiJ hydrogen ie dianaaciiJ. The same 

 tehee place when the gas is brought in contact with a 

 moist body, and what ia remarkable, the selenium pe- 

 netrates the subetsnce, if porous, and communicates to 

 d colour. 



nc acid causes no change on the solution of eaten* 

 iarattad hydrogen in water. 



The solution, when added to the metallic salts, 

 throw* down precipitates from them, which are in ge- 

 aeral black or brown. Those from a salt of sine, man- 

 aad cerium, are however of a red colour. The 

 are considered seleniureU, the latter hydro. 



In another experiment, the prodael fajaaai by pees. 



iog the gas over selsaiusa was dissolved ia water, and 



,i 



the atanatic aad sehaac adds generated, were preetai. 



Uted by aitrate of silver. The precipitete. after the 

 ; was removed by boiling diluted nitric acid. 

 TMM* IJ4 of marietk acid = 40.274 of 



seUniureta, and according to Berseliui, when exposed 

 lo the air, are converted Bio seleniurets of the oxide 

 ef the mctali. 



hydrogen produces rerosrkable effect! 

 of respiration. When admitted into the 

 it excites a painful sensation, and destroys 

 fat several hours the sense of smell, follow, 

 ed by severe eaten h, deep pain of the chest, and ex- 

 pectoration of mucus, having the taste of the vapour of 



,' 



' ' ' ' ' " BBBBBBBBJ . 



These effects are produced by a very minute quan- 

 tity of the gas. Benelius supposes that the seleniu- 

 retted hydrogen is decomposed by the moisture, and 



