1894. | NEW YORK ACADEMY OF SCIENCES. 3 
a:b: c = 0°6223: 1: 04818 and 8 = 86° 41’. The forms 
observed are: m (110) oP; b (010) » Po; p (111) — P; 
= (111) P; the same forms have been observed by Marignac and 
in addition to them c (001) oP was 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 Marignac’s values of the analogous fluostannate are a 
pended for comparison : 
Marignac for 
Calculated. “Found. 3 KF. HF. Sn F,. 
m (110): m/ (110) Gos G3O1397 64° 8/ 
b (010) pa F589) 57 54 
paciiel) ——— a Abie 
p (Il): p? (111) eee 40 37 40 49 
B ae 69 41 69 45 pant he: 
Tap GLA soa (L EL} 42 45 41 15 43 12 
55 (010) 68 37 69 31 aaa 
The salt is stable in dry air but turns brown in moist air, 
being decomposed by water in the following manner: 3KF. HF. 
PbF, 4+nH,O—PbO.H,O+3KF. HF+HF-+(n- 3)H,0. 
The reaction is reversible, for the hydrated dioxide separated 
first is dissolved by hydrofluoric acid and acid potassium fluor- 
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°77 pts. 
HF. instead of the calculated quantity of 20°95 pts. ‘HE. 
The weight of the salt remains absolutely constant even when 
heated at 100-100° for many hours. At 200° hydrogen fluor- 
ide begins to escape, the loss amounting to 1:72 p.c. At 250° 
the loss was 5°43 p. ¢., showing that 1:24 p. e. 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 eaten tem- 
perature some of the salt was placed in a small platizum tube 
closed at one end and dried for several hours at 230-250.° The 
closed end of the tube was heated then with a Bunsen flame. 
Long before the tube became red hot a 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 hydrofluoric acid issued from the nose after 
