A treatise on chemistry / by H.E. Roscoe and C. Schorlemmer.

  • Henry Enfield Roscoe
Date:
1883
Catalogue details

Licence: Public Domain Mark

Credit: A treatise on chemistry / by H.E. Roscoe and C. Schorlemmer. Source: Wellcome Collection.

    499/520 (page 487)
    and a red-purple colour can be obtained. The exact nature of the gold compound which produces the ruby colour in glass is not yet known, nor can we explain why the glass becomes red only on a second heating. Some suppose that the colour is due to metallic gold in so finely-divided a state that the substance only allows red light to pass through it. The amount of gold contained in ruby glass is very small, amounting to from 005 to 0'06 per cent. 2 95 Copper Ruby Glass. Cuprous oxide also colours glass a fine and intense red, but inasmuch as this compound readily undergoes oxidation and as cupric oxide imparts to glass a light green colour, a reducing agent such as iron-scale is added to the materials. Oxidation is also prevented by poling the molten mass with pieces of fresh wood. The mass on cooling appears of a light green colour, but becomes red on re-heating. The pre- paration of this glass was also understood in early times. Klap- roth found both copper and iron in a sample of old Eoman glass, and in the beginning of the 17th century Keri described a method of calcining copper in order to colour glass, and stated that iron- filings, iron-scale, or other reducing agents must be added in order that the colour may come out a bright red. Kunkel also employed himself with the preparation of this glass, but in later times the art of producing red glass without purple of Cassius was lost, and it was not until the year 1828 that Engelliardt examined the question and obtained a prize which the Berlin Polytechnic Society had offered for the discovery, since which time the method has been generally practised. Cuprous oxide possesses a very strong colouring power, and for this reason copper-ruby is generally used for flashing or casing. Perric oxide (colcothar) also imparts a red colour to glass, but one less brilliant than the two preceding ones. Yellow Glass is prepared by the addition of potassium anti- moniate or of antimony-glass, a fused and imperfectly oxidized sulphide of antimony, which imparts to glass a topaz-like tint. Other yellow colours are obtained by the use of silver chloride and silver borate. Organic bodies also impart a yellow tint to glass. This must have been observed by Thomas Aquinas, who describes a mode of preparation of artificial topaz by placing a piece of aloe-wood over the vessel in which the glass is melted. It was formerly believed that this brown colour was due to carbon. Splitgerbe has, however, lately shown that it is caused by the presence of the sulphides of the alkali metals obtained