火试金需要使用什么天平

火试金使用的天平和砝码，应至少对0.005mg敏感。

火试金法（干法）用于定量测定，其中通过加热将一种或多种金属从矿石的其他成分中分离出来，并称量适当的焊剂，以确定矿石中存在的金属量。该方法主要用于测定相对容易还原的有色金属。

金和银的火试金主要取决于以下几点
1、这些金属在熔融金属铅中的溶解度极高，并且在适当成分的熔渣中完全不溶。
铅和炉渣这两种液体的比重相差很大，这使得含贵金属的合金能够从炉渣中分离出来。
事实上，铅实际上可以通过完全控制的氧化熔合从贵金属中完全去除，包括在称为cupel的多孔容器中进行差分过滤。
银的易溶性和金在稀硝酸中的完全不溶性
对于含有非金属元素的矿石冶金产品，该工艺包括两种液体的生产，液态铅含有有价金属，液态渣含有脉石。通常需要添加银（在已知银含量的石英中），以帮助黄金的回收，减少金杯中黄金的损失，并使后续操作有效。
ALLOYGangue–矿石的土质部分，形成易熔熔渣，在还原时从金属部分流出。贵金属——具有很高的道德品质——异的熔渣——熔剂与不熔或难熔体融合产生的易熔化合物。试剂助焊剂是一种物质，当与一些
难熔化合物要么在其中结合，要么将其溶解，在每种情况下都会产生一种化合物或混合物，这种化合物或混合物在普通炉膛温度下很容易熔化。
火试金中使用的主要焊剂和其他试剂如下：
1） 硼砂和硼砂Glas–这些是活性且易于熔融的酸助熔剂。这些降低了熔渣形成的温度，被认为是金属氧化物的良溶剂。这些用于防止在低于初始熔融温度的温度下气体逸出导致矿石损失。
2） 二氧化硅–酸性试剂，与金属氧化物结合形成熔渣，保护坩埚免受腐蚀。
3） Litharge–碱性试剂，有助于酸性物质的融合。减小后，它为按钮提供导线。
4） 纯碱–基本助焊剂，熔融时非常流动，可容纳不可悬浮的细磨不熔材料。在某种程度上，它与金属硫化物反应生成碱性硫化物和硫酸盐。
5） 面粉——强大的还原剂，可减少铅的含量，以收集金银。

6） 硝酸盐–这是一种强大的氧化剂。它氧化硫化物、砷化物、锑化物。当电荷的还原效果较高时，

1、灰吹炉、天平和砝码-应至少对0.005 mg敏感。它的容量不需要超过1000克，但应精度到该负载。

3、砸样台、装样台

4、钢模

5、黏土坩埚、镁砂灰皿

6、炉底板

Fire assaying (dry method ) is applied to the quantitative  determination in which a metal or metals areseparated from the other components of the ore by heat and suitable fluxes are weighed in order todetermine the amount metal present in the ore. This method is applied principally to the determination ofnoble metals that are comparatively easy to reduce.
he fire assay of gold and silver depends mainly upon the following
1. The very great degree of solubility of these metals in molten metallic lead and  theiralmost complete insolubility in slag of suitable composition.
2. The big  difference in specific gravity between the two liquids, lead and slag,  whichpermits the completion of the separation of the precious metal-bearing alloy from theslag.
3. The fact that lead may be practically completely removed from the precious metals by acarefully controlled oxidizing fusion, involving differential filtration in a porous vesselknown as cupel.
4. The ready solubility of silver and the complete insolubility of gold in dilute nitric acid

With ores metallurgical products containing non-metallic metal elements the process consistsbriefly, in the production of two liquids, liquid lead containing the valuable metals and the liquidslag contains the gangue.      It is often necessary to add silver (inquartz with known silver content) to assist in the recoveryof gold, to reduce the loss of gold in the cupel and to permit the subsequent operation to beeffective.
ALLOYGangue – the earthy portion of an ore that forms a fusible slag which flows away from the metallic portion on reduction.Noble metals – having high moral qualities- ExcellentSlag  - the fusible compounds resulting  from the  fusion of  fluxes with Infusible or difficultyfusible bodies. REAGENTS   A flux is a substance which when heated in contact with some          
 difficulty fusiblecompounds either combines in it or takes it into solution, in each case producing a compound ormixtures which is easily fusible at ordinary furnace temperatures.

 The principal fluxes and otherreagents used in fire assaying are the following:
1)Borax and Borax Glas   s – these are active and readily fusible acidfluxes.   These   lower   the   temperature   of   slag   formation   and   areconsidered  excellent  solvent for  metallic  oxides. These  are  used ascover to prevent loss of ore which results from the escape of gas at atemperature below that of incipient fusion.
2) Silica     – Acid reagent which combines with metal oxides to form theslag, protects crucible from corrosion.   
3) Litharge     – Basic  reagent and aids in the fusion of acid substance.When reduced, it supplies the lead for the button. 
 4) Soda Ash     – Basic flux and when molten is very fluid and holds insuspension finely ground infusible materials. To some extent, it reactswith metallic sulfides to form alkaline sulfide and sulfates. 
  5) Flour    – Powerful reducing agent and reduces litharge to lead for thecollection of gold and silver.
 6) Niter     –   This   is   a   powerful   oxidizing   agent.   It   oxidizes   sulfides,arsenides, antimonides. It is used to control size of the button whenthe reducing effect of the charge is high



APPARATUS  

 1. Muffle furnace – oil fired or electric furnace. 

 2. Balance and Weights – should be sensitive to 0.005 mg at least. It need not have a capacity ofmore than 1,000 g but should be accurate with that load.

3. Cupels

4. Iron Mould

5. Annealing Crucible6. Hot Plate