When an alloy is made, it seldom happens that the metal is perfect and compact the first fusion; it is more or less porous, especially when the two metals fuse at very different temperatures. By a second fusion, which usually takes place at a much lower temperature than that requisite for the first, the metal becomes compact and free from pores. This is particularly the case with speculum metal; and I have little doubt it is so with regard to many other alloys. _Alloys of Gold with other Metals._ Gold unites with many of the metals by heat, and forms various alloys, on which it may be proper to make a few remarks. 1. _Gold with platina._ Platina in a small proportion changes the colour of gold towards white. 1 part to 20 gold makes it much paler. 1 to 11 gives it the colour of tarnished silver. 1 part with 4 of gold has much the appearance of platina. The colour of gold does not predominate till it becomes ⁸/₉ of the alloy. The alloy of 1 platina and 11 gold is very ductile, and elastic when hammered. _Lewis. Klaproth. Vauquelin._ 2. _Gold with silver._ These two metals may be combined in almost any proportion by fusion and proper treatment. Homberg found that when equal parts of gold and silver are kept in fusion for a quarter of an hour and then cooled, there were two masses, the uppermost pure silver, the undermost an alloy of 5 parts gold and 1 silver. 1 part silver to 20 gold produces a sensible whiteness in the alloy. 2 parts gold and 1 of silver are stated to form the alloy of greatest hardness; this will consist of 3 atoms of gold to 1 of silver. 3. _Gold with mercury._ See amalgams. 4. _Gold with copper._ Gold and copper form an alloy by fusion together. 11 parts gold and 1 copper form the alloy used for gold coin. The copper heightens the colour of the gold, and makes it harder and less liable to wear. The current gold coin, however, usually contains both silver and copper, but the weight of both does not much exceed one twelfth of the whole. According to Muschenbroeck the maximum of hardness is when 7 parts of gold and 1 part of copper are united. This corresponds nearly to 6 atoms of gold and 1 of copper, the atom of gold being estimated at 66 and that of copper at 56. Other alloys of gold besides the above standard is that for watch cases, which must contain at least ¾ pure gold. Watch chains, and trinkets, are usually made of inferior alloy, called jewellers gold, which is under no control. It rarely contains less than 30 per cent. of pure gold. 5. _Gold with iron._ Gold and iron may be united by fusion in various proportions. 11 parts gold and 1 iron form a ductile alloy which may be rolled and stamped into coin. Its specific gravity is 16.885. The colour is a pale yellowish gray approaching to white. The alloy is harder than gold. When the iron is three or four times the weight of gold, the alloy has the colour of silver. This last compound is constituted of 1 atom of gold and 8 of iron nearly. _Lewis. Hatchett._