18 15.] On Ipdlue. 105 



Phosphorus unites to iodine in dift'ereut proportions, with the 

 (listiigauemeat of heijt, but oK no light. One part of phosphorus 

 and eight parts of ioc'.ine formed a compound of ^ red ori^nge browa 

 colour, fusi'Dle at aliout 212°, and vohitile at a higher temperature. 

 When brought in contact witli water, pl'.osphuj;^eti;d hydrogen gas 

 is disengaged, flocks of j^hosphorus are precipitated, and the water 

 wlkich is colourless contains in solution phosphorous and hydriodic 

 acids. 



One part of phosphorus and 16 of iodine, produce a matter of 

 a greyish black colour, crystallized, fusible at 84°. The hydriodic 

 acid produced by bringing it in contact witli \yater, is colourless, 

 aud no phosphureted hydrogen gas is disengaged. 



One part of phosphorus and 24 of iodine produced a black sub- 

 stance, partially fusible at 115°. Water disbolves it, producing a 

 strong heat, and the solution had a very deep brown colour, which 

 was nor removed by keeping it for some time in a gentle heat. The 

 proportion of one phos-phorus and 16 iodine, results from the ratio 

 between phosphorus and iodine, on the supposition that the phos- 

 phorus is converted into phosphorous acid. One phosphorus and 

 21 iodine should have given me colourless hydriodic acid, on the 

 sujjposition that the jiiiosphorus was converted into phosphoric acid.* 

 1 had indeed ascertained that phosphorous acid converted iodine 

 into iiydriodic acid ; but tlie efl'ect stoj^s or becomes very slow, 

 before all the phosphorous acid is destroyed. This is the reason, 

 that with the proportion one phosphorus and 24 iodine, we obtain a 

 deep coloured acid. It holds a considerable quantity of iodine in 

 solutioJi. We see likewise, that if there tbrm only phospiiorous 

 acid, when the phosphorus is in excess, tliere is formed on the con- 

 trary phosphoric acid, wlicnever ti)e iodine is more than IG times 

 greater than tlie pl.osphorus. 



With I ]jliosp!iorus and 4 iodine we obtain two compounds 

 very different from each other. One of thorn has the same colour 

 as tiiat formed of one pliosphorus + 8 iodine, and seems to be 

 ^he same with it. It melts at 2l7-i-°> sind when dissolved in water 

 give's a colourless iiydriodic acid, phosphureted hydrogen, and 

 phospliorus, which precipitates in orange yellow flocks. The other 

 compound is reddish brown, does not melt at 212", nor at a con- 

 siderably iiigher temperature. Water has no sensible action on it. 

 I'otasli dissolves it witli the disengagement of phosphureted hydro- 

 gen gas, and when ddorine is poured into the solution it shows 

 only iiaces of iodine. When heated in tlie open air, it takes (ire, 

 and bums like ))hosphorus, emitting white vapours without any 

 iodine. 1 condensed these vapours in a moistened glass jar, and I 

 could not perceive any iodine among them. This red substance is 

 always obt lim-d when the ph()sphoruc5 is in the proportion of one to 

 four of iodine. I am Induced to consider it us identical witli that 



• I have »ui»|iiin<l ill dulurniiirnif: (lK»e prnpnrtiiuis, tlial 100 of pliiupliorus 

 rouibriic with lOU oxygi-ii (u luitii [>lii>k|)liurvu< avid, tin 1 widi \M to i'onu [>liu«- 

 j^lioric iiiid. 



6 



