724 GOLD ASSAYING 



quality of gold was introduced called the new standard, but it was found too soft for 

 general use. 



In 1798 a lower standard of gold, consisting of 18 carats pure gold out of the 24, 

 was allowed by the Act, indicated by the stamp of a crown and 18 instead of the lion 

 passant. In 1854 inferior qualities of gold were legalised to be stamped in figures 

 setting forth the fineness viz. 15, 12 and 9 carats pure gold out of the 24. 



It may be well to state for the information of the public, and to put people on their 

 guard in purchasing gold that whether of the best or worst quality, it is still termed 



so and sold as warranted gold, although the value ranges from 85s. to 30s. per oz. 



that 24-carat, or pure gold, is worth 41. 4.. 11 $d. per oz. ; 22-carat, or standard, is 

 worth 31. 17s. lOjd. per oz. ; 20-carat (Ireland only) is worth 31. 10s. 9d. per oz. ; 18- 

 cjw.it is worth 31. 3s. 8%d. per oz. ; 15-carat is worth 21. 13s. Id. per oz. ; 12-carat is 

 worth 21. 2s. 5%d. per oz. ; 9-carat is worth ll. 11s. IQ^d. per oz. 



Hence any purchaser may tell by the stamp the intrinsic value of the article offered 

 for sale, to which must necessarily be added the cost of manufacturing. The marks 

 thus affixed to the article by the Government Assay Offices afford the surest guarantees, 

 and have never before been questioned. It is true a slight variation of a few grains 

 may be detected in assaying a finished piece such as a watch-case, but this arises 

 from the solder employed in putting the object together. 



GOXiD ASSAYING. This may be conveniently divided into : 1. The assaying 

 of gold ores ; 2. The assaying of gold alloys. 



1. The Assaying of Gold Ores. a. Quartz and Earthy Substances containing 

 Gold. The ore is reduced to fine powder and passed through a sieve of 80 holes to 

 the linear inch, and any residual gold is carefully collected, rolled up in a convenient 

 quantity of lead, cupelled (for a description of the process of cupellation and the fur- 

 nace employed, see SILVER), and the resulting button of metal treated in the same 

 manner as those subsequently obtained from the assay of the sifted portion. The 

 total weight of the sample is ascertained in order that the proportion of gold and 

 silver obtained from the residual metal may be calculated. The sifted portion is well 

 mixed and submitted to assay as follows: From 500 to 1,000 grs. of the ore are 

 weighed out and mixed with from 600 to 1,200 grs. of dried carbonate of soda, 500 grs. 

 of litharge or red lead, and 20 grs. of charcoal -powder. The mixture is placed in a 

 Cornish or earthen crucible, and then submitted to a gradually increasing heat in an air- 

 furnace, heated with coke or other suitable fuel, until fusion is completed in from 20 

 to 30 minutes. Considerable effervescence will occur at the first part of the operation, 

 from the escape of carbonic acid gas ; when tranquil the crucible is removed from the 

 furnace and its contents poured into an iron ingot-mould (Jig. 534, Art. COPPER), 

 and when cold the slag is detached from the button of lead. The lead is cupelled 

 (see SILVER), and the button of gold and silver weighed in a balance, turning with 

 Y^oth of a grain. After weighing, the button is rolled up along with 2 times its 

 weight or less of silver, in from 10 to 50 grains of lead, re-cupelled, and the alloy 

 obtained flattened out under a hammer, parted, and the gold weighed. After correc- 

 tion for the silver contained in the litharge or red lead used for the assay, the amount 

 of silver present is ascertained by deducting the weight of the gold from the weight of 

 the silver and gold previously found. For fusion, part of the carbonate of soda may be 

 replaced by calcined borax; the boro-silicates produced being more fusible than silicates. 



b. Auriferous Pyrites with or without Vein- Stuff and Earthy Matters. 1,000 grs. of 

 the finely-powdered ore are to be taken, and calcined in a roasting-duh in a muffle, or 

 in an earthen crucible, in an open air-furnace. The heat is carefully regulated at 

 first to prevent softening of the particles or clotting, and the calcination continued, 

 with frequent stirring, until the smell of sulphurous acid ceases. When cold, the 

 calcined ore is mixed with about 500 grs. of dried carbonate of soda, from 300 to 400 

 grs. of calcined borax, 500 grs. of litharge or red lead, and from 30 to 60 grs. of char- 

 coal-powder, according to the proportion of oxide of iron present. Fusion is conducted 

 in an earthen crucible, and the assay completed as previously described (a). Sand 

 may be used in place of borax, and is cheaper. When arsenic is present, it is only 

 partly expelled by calcination. A piece of iron is therefore added during fusion, and 

 the speiss obtained detached from the button of lead before cupollation. When copper 

 pyrites is present the addition of more litharge or red lead is required for fusion to 

 remove the copper during cupellation. In England and Australia the gold and silver 

 results obtained from the assay are reported to ounces, pennyweights, and grains troy 

 upon the statute ton of 2,240 Ibs. 



c. Assay in the ' Washing-bowl,' Tin-dish, or other Vessel. This method is often 

 resorted to in prospecting at the diggings, and under other circumstances, to ascertain 

 the approximate quantity of gold (native gold) present in a sample of quartz or other 

 ore. The ore is finely powdered, and from 1,000 to 7,000 grs. ( = llb. avoid.) are 

 thrown upon the washing vessel, and thoroughly wcttod with water. The muddy 



