New York Academy of Sciences

TRANSACTIONS

OF TIIE NEW YORK ACADEMYOF SCIENCES,

October 1st. 1894.

The meeting was called to order by President Rees, fourteen persons being present. The minutes of the last meeting were read and approved. The Secretary presented the following nominations for resi- dent membership : Mr. John Jacob Astor, Mr. J. C. Pfister, and on motion they were referred to the Council. The Secretary presented the name of Prof. Bohuslav Brauner, Ph. D., of Prague, Bohemia, as a corresponding member, and on motion the nomination was referred to the Council. The following paper, which had been transmitted to the Academy through Dr. H. Carrington Bolton, was then read.

ON FLUOPLUMBATES.

BY BOHUSLAVRRAUNER, PH. D., PROFESSOROF CHEMISTRY IN THE BOHEMIANUNIVERSITY, PRAGUE. I beg to lay before the Academy a short account of a new series of salts of tetratomic lead, a work which was begun in the Owens College, Manchester, in 1881, and which at intervals has occupied my attention several years. TRANSACTIONSN. Y. ACAD.Scr., Vol. XIV., Sig. 1, Nov. 20,1694. 2 TRANSACTIONS OF THE [OCT. 1,

The first member of the series of$uopZunibates, deriratives of fluoplumbic acid, is the potassium salt described below ; it has been obtained by the following methods : I. By treating the freshly precipitated oxide Pb,0,,3€120 which was first described by me in 1885 (Royal Society of Bohemia 295-299),as the intermediate compound between Pb,O, and Pb,O,, with hgdrofluoric acid and potassium hydrogen fluoride. A mixture of lead fluoride and the crystalline fluoplumbate is obtained, the latter being separated from the former by recrystallization from hydrofluoric acid. 2. By substituting fluorine for oxygen in Fremy’s potassium plumbate, the crude salt containing potassium and lead dioxide in the proportion of 3K,O : PbO, is dissolved in hydrofluoric acid, and from the filtered liquid crystals separate out, which, if necessary, may be purified by recrystallization from hydrofluoric acid. 3. By dissolving lead tetra-acetate Pb(C,H,O,), in hydroflu- oriu acid containing acid potassium fluoride. On spontaneous evaporation of the solution, needle shaped crystals of the fluoplumbate are obtained. The salt has the composition : 3KF.HF.PbF4, being tripotas- sium-monohydrogen orthofluoplnmbate, as proved by the following analytical data.

Calculated for 3KF.HF.PbF4. Found.

f--- f--- (------7 1. 11. 111. IV. V. 3K. .. .111.42 24.60 24-57 - 24.53 - - Pb:. . .206.9 43.35 43.41 43.36 43.35 - - 8F. . . .152*0 31.84 - 31.23 - 31.65 - H. .. . 1.0 0.21 - c - - 0.22 ~- 417.32 100.00

The analysis shows that the substance contains no oxygen. The crystallographic examination of the salt was, in so far of theoretical interest, as Marignac has described a perfectly analogous compound of quadrivalent tin, namely 3KF.HF.SnF,, for it shows that both salts are Bomorphous. The cryatals were examined by Prof. Ch. Tirba of our University, but unfortun- ately their faces are uneven and corroded, ao that no absolutely exact crystallographic and optical examination could be made. Assuming the monoclinic symmetry as has been assumed by. Marignac for the fluostannate, the elements are approximately : 1894.1 NEW YORK ACADEMY OF SCIENCES. 3

a : b : c =Z 0.6223 : 1 : 0.4818 and P = 86O 41’. The forms observed are: m (110) 0oP; b (010) mPA; p (111) - P; (11 1) P ; the same forms have been observed by Marignac and in addition to them c (001) OPwas found by him. The angles calculated from the above axial relations for the normals of the planes are given below together with the inclinations observed and Rlarignac’s values of the analogous fluostannate are ap- pended for comparison : Marignac for Calculated. Found. 3 KP. HF. Sn F,. m (110): mr (110) 63” 42/ 63O 39’ 64O Sf b (010) - *58 9 57 54 p (111) - *46 7 - p (111): pf (111) - 40 3‘1 40 49 : b (010) 69 41 69 45 - pi): (111) 42 45 41 15 43 12 : b (010) 68 37 69 31 - The salt is stable in dry air but turns brown in moist air, being decomposed by water in the fo1:owing manner: 3KF. HF. PbF,+nH ,O=PbO.H,O+3KF.HF+HF+(n-3)H,O. The reaction is reversible, for the hydrated dioxide separated first is dissolved by hydrofluoric acid and acid potassium flyor- ide, and consequently complete decomposition takes place only in presence of a large quantity of water. The above reaction was used only for the analysis of the salt. It was also proved that on decomposition with water, 5 mols. HF are set free, for 100 pts. of the salt yielded in this way 20.’iy pts. HF. instead of the calculated quantity of 20.95 pts. HF. The weight of the salt remains absolutely constant even when heated at 100-looo for many hours. At 200° hydrogen fluoride begins to escape, the loss amounting to 1.72 p. c. At 850° the loss was 5.43 p. c., showing that 1.24 p. c. of the total of 7.96 p. c. of the available quantity of “active” fluoride has been given off. In order to study the behaviour of the salt at a higher temperature some of the salt was placed in a small platimm tube closed at one end and dried for several hours at 230-250.O The closed end of the tube was heated then with a Bunsen flame. ‘ Long before the tube became red ~ota gas began to be evolved having the characteristic odour of fluorine and liberating iodine in crystals from potassium iodide paper held at the exit of the gas. Fumes of hydro0uoric acid issued from the nose after 4 TRANSACTIONS OF THE [OCT. 1, inhaling and eshaling the gas. Some small crystals of silicon were placed in the open end of the tube, and when the closed encl of the tube was heated the silicon burnt with vivid incandes- cence and even with explosive violence (Moissan’s test for fluorine). The residue is white or slightly yellow but care must be taken to exclude-moisture, for when water vapour comes into contact with the heated salt, hardly any fiuorine is given off, and a brown cleliqnescent residue is left. This esperiment has been repeated sereral times, and it con- firms the accuracy of the results obtained by me 13 years ago, viz.: that fluorine may be obtaincd on heating some higher fluorides. Although Moissan has since then obtained free fluorine by a physical method. we have here the first triist- worthy chemical process of obtaining this gas. If potassinni fluoplumbate loses its hydrogen fluoricle at about 230° without losing more than traces of fluorine, one gram of the salt should yield on heating 47 c. c. of fluorine which could be freed from any hydrogen fluoride present by passing it over potassium flnoride, according to Moissxn. Qualitative esperiments have shown that a whole series of jluoplztmbates exist, the metals forming them being the same as those in Marignac’s series of flnostannates, but unfortun- ately the work is connected with great experimental difficulties, for some of the salts we clecomposecl by moisture as soon as they are taken out of the mother liquor.

FLUOPLUMBIC ACID AND LEAD TETRAFLUORIDE. Fluoplumhic acid is obtained either on dissolving some forms of hydrated lead dioxide in hydroflnoric acid or on dissolving lead tetra-acetate in strong hydroflnoric acid, acetic acid being liberated in this case, for on adding soluble fluorides to this solution it gives the corresponding fluoplumhates. This solution, however, cannot be evaporated to dryness, even at the ordinary temperature, a crust of the brown lead dioxide being deposited. In order to prepare anhydrous lead tetraJluoride potassium fluoplumbate was reduced to a fine powder in a platinum basin, using a small platinum crucible as a pestle; a dry‘agate mortar cannot be used, for in contact with silica the salt gives silicdn tetrafloride, water being formed which- at once decomposes the salt. The powdered salt (0.874 grm.) was then thrown on the surface of cold, concentrated sulphuric acid (5 cc.). Hydrogen fluoride at once escapes and a pale yellow solution is obtained, having the same characteristic color as that of lead tetrachlo- 1894.1 NEW PORK ACADEMY OF SCIENCES. 5

ri(le, which mas isolated by Friedrich in this laboratory. Dense f'uines soon begin to come otf, having an extremely pungent smell which resembles that of free fluorine. They seem to contain some gaseous lead tetrafluoride. After the salt has completely dissolved in the acid : 3KF.HF.PbF4t 3H2S0,= 4HFt3KHS04+PbF4, the clear yellow liquid begins to get turbid, and after half an hour or so it is converted into a thick lemon-yellow jelly. From this emulsion, which probably contains the colloclial modification of lead tetrafluoride, the latter cannot be separated at the ordiiiary temperature. On heating the mass to loo0, some hydrotlooric acid escapes, and n heavy, lemon-yellow powder is deposited on the bottom of the crucible, this probably being another modification of lead tetrafluoride. The sulphuric acid could be easily poured off from the yellow precipitate, and it mas found that the acid contains no lead in solution. The yellow powder could be washed with sulphuric acid by decantation, and no apparent change took place on heating the m(xture to looo. But as soon as it was heated to 115O, complete decomposition took place and white lead sulphate was left at the bottom of crucible : PbF4+H,S04=PbS04S2HFS F 2 m. I have not yet been able to isolate lead tetrafluoride, in spite of numerous attempts, as no liquid could be found which would displace the sulphuric acid without at the same time decompos- ing the tetrafluoride. Dry plates of plaster of Paris absorb the greater part of the acid, but not all, and after some time decomposition t&es place and the brown dioxide is formed : PbF,+ 2H20=Pb02+4HF. Hydrofluoric acid dissolves it partly and the solution contains fluoplumbic acid, for it liberates iodine from potassium iodide, etc. I On comparing the properties of the incompletely studied lead tetrafluoride with those of lead tetrachloride, which I often had an opportunity of observing, as it was discovered by Friedrich in this laboratory, it will be seen that both substances are set 'free from their double salts by strong sulphuric acid, without being decomposed by it. The tetrachloride is R liquid, whilst the tetrafluoride seems to exist in several .forms. I hope to be able to throw some light on the tetrafluoride of lead by a com- parative study of the anhydrous tetrafluoride of tin.

LEAD DISULPHATE. Potassium fluoplumbate was dissolved in a very large excess of cold sulphuric acid so that even after several days no separa- 6 TRANSACTIONS OF THE [OCT. 1, tion of tetrafluoride kook place. The clear, yellow liquid gave off dense fumes, smelling of fluorine, in large quantitg. The solution was heated for several days in a coverccl crncible on the water bath, then allowed to stnncl in a dessicator aqd heated again, and this alternative process was repeated cluring several weeks. The solution was found to give off a smell of hyclro- fluoric acid and an orange-yellow crystallinc substance was separated slowly, but only after standing for about two months the solution became colourless and free from an1 dissolved tetrafluoride. After this time the solid orange-coloured substance was washed with sulphuric acid by decantation. The acid mas then poured off as completely as possible and the substance was decomposed with water, when it yielded lead dioxide and a solution containing sulphuric acid but only a small quantity of hgdrofluoric acid. The substance can be therefore onl~7 lead disulphate Pb (SO,),, analogous to Sn (SO,), and the formation requiring a very long time, must have taken place according to the following equation : PbF,+nH,SO,=Pb(S0,),+4 HF+(n-2)H2S0,. The more the quadrivalent lead is studied, the greater becomes its analogy with quadrivalent tin and of course the existence of the substances described in the present paper gives additional confirmation to the position which lead occupies in Mendelejeffs periodic system. Thirty years ago hardly anyone could have predicted that lead would form compoiinds anslo- gous not only with those of tin, but also with those of silicon, titanium, ziconium, cerium and thorium. May, 1894.

Prof. Hubbard exhibited some gnawed beaver sticks from the pond described by him last year (Trans., Vol. XIII., 115,177) and commented upon them. Reports of summer work were then presented by the following members : Osborn, Britton, Martin, Hallock, van Ingen, Kemp, Cox, Pupin and Re&, after which the Academy adjourned. J. F. KEMP, Recording Secretary.