1869.] Physics. 565 



time of our informant's visit, several others being, however, rapidly- 

 fitted for use. Each furnace has its fire-box so arranged as not 

 only to heat the retort which holds the manganate of soda, but also 

 one or more chambers through which an aii-blast passes to the 

 retort. The retort furthermore communicates, by a pipe furnished 

 with stop-cocks, with a suitable steam boiler. About 600 pounds of 

 manganate of soda are placed in the retort, heated to the requisite 

 degree in the furnace ; superheated steam from the boiler is then 

 admitted for about ten minutes. Two equivalents of the manganate 

 of soda and two of water react upon each other, and the operation 

 proceeds as described above. 



A method of coating glass, porcelain, or earthenware, with a 

 thin film of lustrous metallic platinum, has been published by Prof. 

 Boettger. Dry chloride of platinum, freed from excess of acid, is 

 mixed in a small porcelain mortar, with essential oil of rosemary, 

 until the original brown-red colour of the salt has entirely dis- 

 appeared, and has been converted into a black pitch-like looking 

 mass. When the pitch-hke mass has been obtained, the oil is en- 

 tirely removed, and the pasty mass is mixed with at least five times 

 its weight of lavender oil, and mixed therewith to a homogeneous 

 fluid ; this, after having been quietly standing for half-an-hour, is 

 applied with a hair brush on the glass or porcelain objects to which 

 it is desired to give a coating of lustrous platinum, and after the 

 very thinly and evenly laid on film is dry, the objects are either 

 I^laced in a red-hot mufile, or heated in the flame of a glass-blower's 

 lamp, care being taken not to exceed a red heat. 



According to M. Grimm, chloride of copper completely removes 

 even fi:om coloured woven cotton tissues, stains occasioned by 

 nitrate of silver ; the tissue is to be afterwards washed with a 

 solution of hyposulphite of soda, and next thoroughly washed with 

 water. From white cotton and linen tissues, nitrate of silver stains 

 are more readily and efi'ectively removed by applying dilute solu- 

 tions of permanganate of potassa and hydrochloric acid, followed by 

 washing with hyposulphite of soda solution, and rinsing in jjlenty 

 of fresh water. By these means the use of the highly poisonous 

 cyanide of potassium is rendered unnecessary. 



Heat. — In the course of an introductory lecture on the occasion of 

 the opening of the new laboratories at Berlin, Dr. Hofmann, F.K.S., 

 illustrated some new experiments with flame, which he had devised 

 for the purpose of showing its structure. Take a piece of canvas 

 and put it on to the top of the glass chimney of an argand gas- 

 burner, taking care to envelop the glass chimney previously with a 

 very thin piece of copper foil, while the access of air at the bottom 

 of the burner should be as much as possible prevented. On turning 



