BISMUTH IODIDE AND BISMUTH FLUORIDE. 137 X.-CONTRIBUTIONS FROM THE LABORATORY OF GON-VILLE AND CAIUS COLLEGE CAMBRIDGE. No. XI.-Bismuth Iodide and Bismuth Fluoride. By B. S. GOTT B.A. Scholar of Gonville and Gains College and M. M. PATTISON MUIR M.A. Bismuth Iodide. IT is known that bismuth iodide Bi13 may be prepared either by heating together bismuth and iodine in the ratio Bi 31 or by adding an aqueous solution of potassium iodide to a solution of bismuth nitrate in dilute nitric acid. The directions given by earlier experi-menters for preparing this compound in the wet way are vague. We have recently made some experiments on the preparation of bismuth iodide and also on the comparative stabilities towards water of this compound according as the specimen is prepared in the dry or the wet may.Preparation of Bismuth Iodide in the Wet Way.-Excess of a fairly concentrated aqueous solution of potassium iodide is added to bismuth nitrate dissolved in the smallest possible quantity of dilute nitric acid ; BiI is thus precipitated along with iodine. The precipitate is dis-solved in as small a quantity as possible of concentrated aqueous hydriodic acid and water is added until the greater part but not the whole of the bismuth is precipitated as brown BiI,. The solid matte 1.38 GOTT AND MUIR BISMUTH IODIDE is collected and dried for some time a t loo" whereby most of the free iodiue is volatilised. The residue is then washed once or twice with absolute alcohol and finally dried a t 100". Some Properties of Bism.uth Iodide.-The salt prepared as described above is somewhat soluble in absolute alcohol ; 100 parts by weight of alcohol at 20" dissolve about 3$ parts of the salt.The sp. gr. of BiI prepared in the dry way was found to be 5.64 20" 'LO" ' a t - and the sp. gr. of BiI prepared in the wet way was found 20" to be 5.65 at -. 20" Specimens of the iodide prepared in both ways were treated with water in about the ratio BiI 3000H20 for different times and at different temperatures ; the amount of decomposition to BiOI and HI was determined by measuring the quantity of hydriodic acid produced a t the expiration of fixed times. The results were as follows :-Temperature = 36O-After 30 ininuteu' action . . 3 ) 60 7 7 7 7 * . a * 7 7 150 7 ) > 7 -. > 7 60 7 9 7 7 .' . * , 150 9 ' 7 ) - * Temperature 60-65". After 30 minutes' action . . Temperature = 100'. After 30 minutes' action . . 97 7 ) Y ) * * * )) 160 )) )) BIT prepared in the dry way. 17 * 5 p. c. decoinposed 19.8 7 ) 24 -4 > 7 22 -5 9 ) 26 *4 7 ) 22 -75 7 ) 35 *1 7 7 30 -7 7 7 27 *4 ) Y BIT prepared in the wet way. 17 -7 p. c. decomposed 19 *.2 97 23 *9 7 ) There is therefore no appreciable difference between the rate of decomposition by water of the two specimens of bismuth iodide. Bismuth Fluoride BiF (comp. Pattison Muir Hoffmeister and Robbs, Trans. 1881 39 33). Prejm-ation.-(l.) Moist freshly precipitated Bi,03,xH20 is added little by little to hot hydroflnoric acid in a platinum dish so long as the oxide dissolves fairly easily ; the liquid is evaporated to dryness at loo" and the residue is heated to bright redness in a closed platinum crucible.If the addition of bismuthous oxide to hydro-fluoric acid is continued until some remains undissolved or if the solution of the oxide in the acid is boiled for some time a considerabl AND BISMUTH FLUORIDE. 139 quantity of a double compound of bismuthyl fluoride and hydro-flnoric acid BiOP,BHP is produced :-Bi,Os + 6HF = 2(BiOP,2HF) + H,O. (2.) A fairly concentrated aqueous solution of potassium fluoride is added to bismuth nitrate dissolved in the minimum quantity of dilute nitric acid until the whole of the bismuth is precipitated. The precipitate is washed repeatedly with cold water and is then sus-pended in boiling water which is changed from time to time until no trace of potassium salt is to be found in the washings.This salt, after drying at loo" is pure bismuth fluoride BiF,. Bismuth fluoride is a heavy crystalline compound sp. gr. -5.32. It is unchanged on heating to fusion (about a full red heat). The salt is insoluble in water or alcohol; it does not react with sulphur when the two are heated together ; it is not changed by heat-ing in the mixture of nitrogen oxides produced by warming starch with nitric acid. Bismuth fluoride is the most stable of all bismuth haloid compounds. 20" -20" Preparation of Bismuthyl Fluoride BiOF. Moist freshly precipitated Biz03,xHz0 is added to hot hydrofluoric acid until all acid reaction has disappeared. The solid thus produced is washed with hot water dried at looo find afterwards heated to moderate redness in a closed platinum dish ; or the solid is suspended in boiling water which is changed from time to time until the wash-ings are perfectly neutral to litmus and the residue is then dried at 100". Bismuthyl fluoride is a heavy white crystalline powder; sp. gr. 2oo - - 7.5 whether prepared by removing all HF by long continued SO" washing or by heating. It is not changed by heating to moderate redness but if the temperature is raised to bright redness decom-position occurs. We are now engaged with an examination of the double compounds formed by the union of bismuth haloid salts with the haloid salts of the alkali metals ; the results we hope will throw some light on the questions suggested by the term moZecuZar com-pounds