‘Twenty-four carat’ was taken as the standard of pure gold because the Roman gold solidus weighed twenty-four carats (each 1/144 of an ounce). The assayer’s carat is 1/24 part divided into four assay-grains. Medieval gold coins such as Edward III’s noble and the Venetian zechin, always of the same quaint pattern, were generally twenty-three carat 3-1/2 grains fine, = 995 parts in 1000. But this nearly pure gold being very soft, it became customary to alloy the metal with a certain amount of copper to give it the hardness necessary for trade purposes in modern times. Sovereigns or Unites were coined under James I at 172 grains, under Charles I at 141 grains. Their value in silver varied of course according to market-rates for gold. Coined under Charles II at 130 grains they were henceforth called Guineas, varying in value from 30 to 20 shillings. Repeated attempts to fix their value by law utterly failed. In the eighteenth century it was generally above the 21_s._ standard at which the guinea is still reckoned as a polite coin. In 1816, on the adoption of a gold standard, the name of Sovereign was revived for the coin which is its basis. The sovereign weighs 123·274 grains, of which 113·006 are pure gold. It is light if it weighs less than 122-1/2 grains, that is if it has lost more than 1-1/2_d._ in value. Its life of current weight is about 20 years in ordinary circumstances of circulation. The mint value of gold is £3 17_s._ 10-1/2_d._ an ounce Troy; that is 2·1212 pence a grain pure, or 1·7676 penny at the standard fineness of 22 carats = 916·6 in 1000. France adopted a gold standard in 1855; other countries followed. The United States adopted it in 1900. The sovereign is coined at full value without ‘seigniorage.’ In France and other gold-standard countries a charge is made for coining. In France this charge is 6 fr. 70 c. on the kilo of standard gold, 0·900 fine, value 3100 francs; this is equal to 0·216 per cent., so that 20-franc pieces lose 4·4 centimes or nearly a halfpenny each on being melted, besides assay charges. The history of mint-weight will be further told in Chapter XX, section ‘The Carat and the Grain.’ 2. GUERNSEY CURRENCY In this curious relic of the old French monetary system the Livre is the equivalent of the _louis d’or_ of 24 francs; the Sol or sou is a shilling, 1/20 of the livre; the Denier is a penny, 1/12 of the shilling, and it is divided into 8 doubles, each equal to the old French _liard_ or quarter-sou of 3 deniers, not to the old French double of 2 deniers. The only Guernsey coins are the bronze pieces of 8, 4, 2, 1 doubles; that of 8 doubles being the penny. The silver coins are French, counted 10 pence to the franc; so that the five-franc piece passes for 4_s._ 2_d._ Guernsey.