The supervisory lamp associated with the peg in the wanted subscriber's jack glows from the time that the peg is inserted until the subscriber responds, when it darkens, in which condition it remains until the subscriber restores the receiver to the hook and causes the lamp to light up again.
News, 1891, 63, p. 1); just above the boiling point the vapour is orange-yellow, but on continued heating it darkens, being deep red at 50o; at higher temperatures it lightens, becoming straw-yellow at 650°.
The solid melts to a pale yellow liquid which on continued heating gradually darkens and becomes more viscous, the maximum viscosity occurring at 180°, the product being dark red in colour.
The saturated aqueous solution is colourless and fumes strongly on exposure to air; after a time it darkens in colour owing to liberation of iodine.
Silk is readily distinguished from wool and other animal fibres by the action of an alkaline solution of oxide of lead, which darkens wool, &c., owing to the sulphur they contain, but does not affect silk, which is free from that body.