250 ANTIMONY. — Estimation.
Tlie action of the hydrochloric acid is greatly acceler-ated by mixing with it a small proportion of nitricacid. When the solution thus obtained is evaporated,the trichloride of antimony remains in the solid state.To prepare the pure salt, the hydrochloric acid solu-tion of the trichloride should be evaporated in aporcelain dish, till it begins to crystallize on the dishbeing placed in a cold situation; the concentratedliquid is then transferred to a retort, and distilleduntil a drop of the liquid solidifies upon a cold sur-face ; at this point the receiver is changed, and theremaining portion of the charge collected as pure.
It is white, semitransparent, crystalline, of a but-tery consistence, and deliquescent in the air.
When added to water it gives a bulky whiteprecipitate of powder of algaroth, which consists oftrioxide, united with a portion of the trichloride,while hydrochloric acid remains in the solution.
Trichloride of antimony affords, with all the otherreagents, similar reactions to those which distinguishthe other salts of tins metal.
Besides being used as a caustic, it is employed inthe arts, especially by gunmakers, for the purpose ofgiving a yellow colour to gun barrels, and is calledbronzing salt. It is used for this purpose in the stateof solution, mixed with olive oil, and rubbed overthe iron slightly heated, which is then exposed tothe air till the desired colour is obtained. Some-times, to quicken the effect, nitric acid is added.When bronzed, the surface of the iron is polished bya burnisher, or by wax, or by varnish composed of2 ounces of shell-lac and 3 drachms of dragon’s-blooddissolved in 2 quarts of spirit of wine.
Quantitative Estimation of Antimony byAnalysis. —The percentage of antimony in a mineralmay be estimated from the amount of the trisul-pliide of antimony, the tetroxide or antimonate ofantimony (Sb 2 0 4 or Sb0 0 ), or of the metal whichit produces when operated upon with suitable re-agents.
As Trisulphide .—A solution of the metal is ob-tained by treating the ore with strong hydrochloricacid, containing some nitric acid (if silver be absent).This solution is diluted with water, and should anyturbidness ensue, tartaric acid must be added todissolve it; or if the addition of this acid wouldinterfere with the estimation of any other metal,hydrochloric acid is employed to effect the samepurpose. Sulphuretted hydrogen is then transmittedthrough the liquid, until the solution acquires astrong odour of the gas, when the whole of theantimony will be converted into the red trisulphide.If antimony is the only metal present, the vesselholding the precipitate may be placed on a hot sand-bath till the excess of sulphuretted hydrogen isexpelled. By this means the small quantity oftrisulphide retained in solution by the excess of thegas is set at liberty. The solution is then filteredthrough a dried and tared filter, washed with water,dried in a water bath till the weight remains con-stant, and weighed.
As Tetroxide .—As the antimony in solution is oftenin a higher state of oxidation than the teroxide,
especially if nitric acid has been employed, andas more or less of the sulphide of hydrogen isdecomposed by the free acid of the solution beforeprecipitation, the sulphide of antimony producedcontains an excess of sulphur. In this case theexcess of sulphur is to be extracted with carbondisulphide, and the antimony trisulphide introducedinto a porcelain crucible, and then add—first, a fewdrops of sti'ong nitric acid, and then fuming nitricacid in quantity about ten times the amount of theprecipitate, and allow the acid to evaporate graduallyin the water bath. The suljihur separates at firstas a white powder, but is completely oxidized duringthe evaporation. The white residue is antimonicoxide with sulphuric acid, and may be convertedinto the tetroxide (Sb.,0 4 ) by ignition.
As the tetroxide is neither volatile nor decom-posable by a red heat, it affords a very accuratemeans of determining antimony quantitatively. TheSb 2 0 4 contains 79-22 per cent, of the metal.
As Metal .—Having ascertained the weight of thedry trisulphide produced by treatment with acids,and precipitating by sulphuretted hydrogen in theway already pointed out, a known quantity is to betaken and decomposed by heating in an atmosphere
of hydrogen; sulphuretted hydrogen is evolved, andmetallic an timony is left. A convenient apparatus forthis purpose is seen in Fig. 10. The flask, a, containswater and a few bars of zinc; sulphuric acid ispoured in through the funnel, b, in order to generatethe gas, which escapes by a tube opening justbelow the cork of the flask, and which is providedwith two bulbs, c c, where the greater part of the mois-ture carried away by the gas is condensed. To dry thehydrogen completely, it is conducted through anotherlarge tube, d, filled with fragments of chloride ofcalcium, and thence into the bulb, e, holding thesubstance to be reduced.
Before commencing the operation, the bulb, e, withits glass tubes attached, should be thoroughly cleaned,dried, and weighed, and the trisulphide of antimonythen introduced. The bulbed tube and its contentsare now reweighed, and the increase of weight is thequantity of the compound submitted to experiment.The various parts of the apparatus are next well con-nected by means of caoutchouc tubes, as seen in thefigure, and the hydrogen generated; as soon as theapparatus is filled with the gas, a gentle heat is ap-plied by means of a spirit-lamp, g, to the bulb con-taining the substance, till the reduction is completed.If the compound consists of trisulphide of antimony