13 



process was repeated once with fresh acid, somewhat stronger, so as to 

 insure the total removal of the carbonates. Sulphide of hydrogen in 

 excess, added to the acid solution, gave a copious precipitate of sulphide 

 of zinc ; this was removed by filtration, and oxalate of ammonia added 

 to the filtered solution, which threw down a precipitate of oxalate of 

 lime. This shows either that the whole of the carbonate of lime was not 

 removed from the bone during the action of the solution of zinc, or that 

 new carbonate of lime had been formed from the phosphate by the substi- 

 tution of oxide of zinc. The tissue treated with the acetic acid was 

 washed repeatedly with distilled water, and boiled with it, in order to 

 remove all traces of the acetates of zinc and lime, and then dissolved 

 in hydrochloric acid. To this solution ammonia was added in excess, 

 and it was then digested for some hours, so as to insure the re-solution 

 of all the phosphate of zinc thrown down at first. On filtering, the 

 phosphate of lime remained on the filter ; the filtered liquid contained 

 any zinc existing as phosphate ; on adding sulphide of ammonium to 

 the solution, a precipitate of sulphide of zinc was thrown down. The 

 solution filtered from the precipitate of sulphide of zinc, treated with 

 chloride of magnesium, gave a precipitate of ammonio-magnesian phos- 

 phate. On determining the amount of zinc in the precipitated sul- 

 phide in the usual way, and calculating the amount of phosphoric 

 acid in the ammonio-magnesian phosphate, the results showed that 

 the phosphoric acid and oxide of zinc were in the proportions to form 

 the salt 3ZnO,P05. In the air-dried bone, the amount of oxide of 

 zinc as phosphate was 6*090 per cent., equivalent to 10*805 per cent, 

 of 3ZnO,P05. The amount of lime thus substituted by zinc appeared 

 to vary according as the bone was completely enveloped or not, and 

 according to the part of the bone examined. The solid part of a 

 fragment of a small bone, completely enveloped by a coating of hy- 

 drocarbonate about 5°"° thick, contained a quantity of oxide of zinc 

 equivalent to 16 "98 per cent, of phosphate of zinc. A part of the car^ 

 bonate of lime may have been derived from this substitution. Scarcely a 

 trace of the organic matter of the bone had been preserved, but in those 

 which were covered by layers of hydrocarbonate, the inside of the coat- 

 ing or shell of mineral, when removed from the bone, had always a 

 yellowish-brown superficial colour, and bore an accurate imprint of the 

 bone. When the inner layer of such a coating was dissolved slowly in mo- 

 derately dilute acetic acid, brown membranaceous flocculi floated about, 

 which were probably the remains of the periosteum. This would seem 

 to show that the bones were not much decayed before they were en- 

 veloped in the hydrocarbonate of zinc, and consequently confirms the 

 view that the formation of the upper layers, at least, of the hydrocar- 

 bonate of zinc in the cavern, was contemporaneous with the species of 

 animals to which the bones belong. 



Chemical Composition of the Hydrocarhonate of Zinc. — Analyses of 

 the Spanish hydrocarbonate of zinc have been already published by MM, 

 T. Petersen and E. Veit-^', and by M. A. Terreil.f The former believe that 



* Annal. d. PhariB, u. Chem. Bd. cviii. 48. f Compt. rend, t, xlix., p. 553, 



