BOOK Vll. 249 



with the mouth and then a blue flame will be emitted. In the end the tubes 

 are weighed, and if their weights prove equal, he; who has undertaken this work 

 has not laboured in vain. Lastly, both an' placed in another balance-pan and 

 weighed ; of each tube four grains must not be counted, on account (A the 

 silver which remains in the gold and cannot be separated from it. From the 

 weight of the tubes we learn the weight both of the gold and of the silver 

 which is in the button. If some assayer has omitted to add so much silver to 

 the gold as to make it three times the quantity, but only double, or two and a 

 half times as much, he will require the stronger quality of aqua which 

 separates gold from silver, such as the fourth quality. Whether the aqua 

 which he employs for gold and silver is suitable for the purpose, or whether 

 it is more or less strong than is right, is recognised by its effect. That of 

 medium strength raises the Httle bubbles on the tubes and is found to colour 

 the ampulla and the operculum a strong red ; the weaker one is found to 

 colour them a light red, and the stronger one to break the tubes. To pure 

 silver in which there is some portion of gold, nothing should be added when 

 they are being heated in the cupel prior to their being parted, except a bes 

 of lead and one-fourth or one-third its amount of copper of the lesser weights. 

 If the silver contains in itself a certain amount of copper, let it be weighed, 

 both after it has been melted with the lead, and after the gold has been parted 

 from it ; by the former we learn how much copper is in it, by the latter how 

 much gold. Base metals are burnt up even to-day for the purpose of assay, 

 because to lose so little of the metal is small loss, but from a large mass of 

 base metal, the precious metal is always extracted, as I will explain in 

 Books X. and XI. 



We assay an alloy of copper and silver in the following way. From a 

 few cakes of copper the assayer cuts out portions, small samples from small 

 cakes, medium samples from medium cakes, and large samples from large 

 cakes ; the small ones are equal in size to half a hazel nut, the large 

 ones do not exceed the size of half a chestnut, and those of medium size come 

 between the two. He cuts out the samples from the middle of the 

 bottom of each cake. He places the samples in a new, clean, triangular 

 crucible and fixes to them pieces of paper upon which are written the weight 

 of the cakes of copper, of whatever size they may be ; for example, he writes, 

 " These samples have been cut from copper which weighs twenty centum- 

 fondia." When he wishes to know how much silver one centumpondium of 

 copper of this kind has in it, first of all he throws glowing coals into the 

 iron hoop, then adds charcoal to it. When the fire has become hot, the paper 

 is taken out of the crucible and put aside, he then sets that crucible on the 

 fire and gradually heats it for a quarter of an hour until it becomes red hot. 

 Then he stimulates the fire by blowing with a blast from the double bellows 

 for half an hour, because copper which is devoid of lead requires this time to 

 become hot and to melt ; copper not devoid of lead melts quicker. When 

 he has blown the bellows for about the space of time stated, he removes the 

 glowing charcoal with the tongs, and stirs the copper with a splinter of wood, 

 which he grasps with the tongs. If it does not stir easily, it is a sign that the 



