28 
THE VOYAGE OF H.M.S, CHALLENGER. 
of the tube shows the quantity of water collected directly, and the solvent process is now 
complete. The boat is withdrawn from the tube and contains a vitreous mass. The 
silica is separated in the usual way after the evaporation to dryness of an acid solution. 
The iron and alumina are precipitated in the form of hydroxides by ammonia. Ebulli- 
tion is maintained until the complete disappearance of the excess of free ammonia, so 
as to keej) the manganese in solution ; when the latter body was present in rather con- 
siderable quantities, the separation was effected by means of succinate of ammonia. 
The oxides of iron and alumina weighed together are redissolved in hydrochloric 
acid ; the small quantity of silica which is left undissolved in the acid is then treated 
apart, and the weight of it added to that of the silica obtained before. The iron is 
separated from the alumina by potassium hydrate ; to the filtrate, after the separation of 
the iron and alumina, the direct addition of sulphide of ammonium gives a precipitate 
of sulphide of manganese, which is weighed after calcination in the form of mangano- 
manganic oxide. The calcium is afterwards precipitated in the form of oxalate of 
rnlcium, and weighed as oxide of calcium. In the filtrate separated from the precipitate 
of oxalate of calcium, the addition of phosphate of ammonium and ammonia produces 
a precipitate of ammonio-magnesia phosphate. Finally, the sulphuric acid is treated in 
the form of sulphate of barium in the last filtrate. 
The second portion of the substance was destined for the determination of the 
protoxide of iron. The substance, dried and weighed, is introduced into a hard glass 
tube in an atmo.spherc of carbonic acid gas, and mixed with hydrofluoric acid and 
sulphuric acid. The sealed tube is submitted to a temperature of about 100° C. until 
the .sub.stance is entirely decomposed ; the solution is then titrated with permanganate 
of potash. 
The third and last portion of the substance is used for the determination of the 
alkalies. This part, weighed and dried, is submitted to the action of sulphuric and 
hydrofluoric acids in a platinum capsule ; after evaporation with acids and calcination, 
the substance is treated with hydrochloric acid. The manganese is precipitated by 
barj'ta, and the excess of baryta by ammonia and carbonate of ammonia. A solution 
is thus obtained, containing the alkaline chlorides and excess of carbonate of ammonia ; 
the latter is got rid of by calcination. The last traces of magnesia are eliminated by 
oxide of mercury ; the chlorides are weighed together. To the solution containing the 
chlorides of so<lium and j)otassium is added chloride of platinum, in order to separate the 
|K)tassium as chloro-platinate, which is weighed in a gla.ss filter after dessication. From 
the weight of the chloro-platinate of potassium, the quantity of chloride of potassium 
is detluccd. Tlic weight of cliloride of sodium is obtained by difference. 
In certain <mcs, when it bcciimc necessary to estimate quantitatively the various 
substances forming the residue, a large quantity of the deposit was treated with very 
dilute hydnsdiloric acid, Liking care that the operation should take place without 
