| Show heat the invisible radiations from a heated tody possess tho power of effecting certain chemical decompositions much after tho manner of lights as for instance iu photography among the substances sensitive to weak radiations of heat may bo mentioned paper saturated with cn ario bromide or a mixture of sulphate of copper and potassium bromide which has a faint greenish tint that becomes olive brown in radiant heat and if green is used a brown image can be obtained in a minute by exposing to the radiations from a gas stove and on treatment with silver nitrate this imago becomes black by reason of tho reduction of the silver paper is affected by radiant heat as by light and paper impregnated simply with sulphate of copper yields a feeble image which becomes nearly black when treated with silver nitrate A mixture of sulphate of copper and oxalic acid gives a paper which becomes brown on exposure chlorate of copper is also very sensitive tho faint blue color becoming a deep green similarly used bromide of tin behaves as if exposed to light but unexposed parts become very black when treated with silver nitrate nitrate of silver which is markedly acted upon by light is slightly browned when exposed to heat radiation and the tint is deepened by or gallic acid st louis globe democrat |
