_Phosphorus_ occurs in some few glasses in the form of phosphoric acid, and this substance, as such, has no colouring effect. Calcium phosphate, however, is sometimes added to glasses for the purpose of producing opalescence. Its action in this respect is probably similar to that of tin oxide and aluminium fluoride, these substances all remaining undissolved in the glass in the form of minute particles in a finely divided and suspended state. _Arsenic_ does not exert a colouring effect on glass, and owing to its volatile nature it can only be retained in glass in small quantities and under special conditions. A “decolourising” action is sometimes ascribed to arsenic, but if this action really exists it can only be ascribed to the fact that arsenic compounds are capable of acting as carriers of oxygen, and their presence thus tends to facilitate the oxidation of impurities contained in the glass. A further reference to this subject will be found below in reference to the compounds of manganese. _Antimony_, although frequently added to special glass mixtures, does not appear to produce any very powerful effects, except possibly in the direction of producing white opacity if present in large proportions. The sulphide of antimony, however, exerts a colouring influence, although its volatile and unstable character renders the effects uncertain. _Vanadium_, owing to its rarity, is probably never added to glass mixtures for colouring purposes, although it is capable of producing vivid yellow and greenish tints when present even in minute proportions. On the other hand, vanadium occurs in small proportions in a number of fire-clays, including some of those of the Stourbridge district, and glass melted in pots containing this element is liable to have its colour spoilt by taking up the vanadium from the clay. _Sulphur_ is an element whose presence in various forms is liable to affect the colour of glass in a variety of ways. The colouring effects of sodium-, calcium-, cadmium-, and antimony-sulphides have already been referred to. Sulphur probably never exists in glass in the uncombined state at all, but sulphur and its oxides, which are often contained in furnace gases, sometimes exert a very marked action upon hot glass. The presence of sulphur gases in the atmospheres of blowing-holes and annealing kilns is liable to produce in the glass a peculiar yellowish milkiness which penetrates for a considerable depth into the mass of the glass and cannot be removed by subsequent treatment. Glass vessels, particularly if made of glass produced from raw materials among which salt-cake has figured, are also affected by contact with fused sulphur or its vapour, the effect being a gradual disintegration of the glass. The precise mechanism of these actions is not known at present, but they probably consist in the formation of sulphur compounds within the glass, possibly giving rise to an evolution of minute bubbles of gas.