i8 7 i.] 



Chemical Science. 407 



of the Bunsen burner was split and flattened outwards. Fortunately, none of 

 the three persons present in the laboratory at the time were hurt. The author 

 takes the opportunity of referring to a communication of Dr. E. Kopp, bear- 

 ing upon the conditions under which nitroglycerine explodes or burns off 

 quietly. When nitroglycerine is caused to fall drop by drop on a thoroughly 

 red-hot iron plate, it burns off as gunpowder would do under the same condi- 

 tions ; but if the iron is not red-hot, but yet hot enough to cause the nitro- 

 glycerine to boil suddenly, an explosion takes place. 



Dr. Von Kobell gives an account of the testing of various minerals containing 

 lithia with the spectroscope. The author puts the pulverised minerals on a 

 piece of platinum foil formed like a channel, perforated with small holes, and 

 held by means of a pair of platinum forceps. The author observes that, unless 

 the mineral to be tested for lithia is previously well moistened with hydro- 

 chloric acid, the detection of lithia may fail, since only the spectrum of the 

 flame tinged by chloride of lithium exhibits the characteristic line. Several 

 minerals have also been tested by this author for thallium, and more especially 

 some zinc ores. Most of these minerals gave a negative result ; but the spha- 

 lerite (a kind of zinc blende) from Geroldseck, and a similar mineral from Her- 

 besthal (a small Prussian village close to the Belgian frontier), gave very evi- 

 dent indications of the presence of thallium. 



The popular toy, "Pharaoh's Serpents," has gone almost out of use, owing, 

 probably, to the poisonous nature of the ingredients and the danger of inhaling 

 the mercurial fumes they evolved. Dr. Puscher has published the recipe for a 

 mixture for producing so-called Pharaoh's Serpents which are not attended 

 with injurious fumes. Mix intimately together 2 parts of bichromate of 

 potassa, 1 part of nitrate of potassa, and 3 parts of white sugar. This mixture 

 should be pressed in paper or tinfoil cones, and, if intended to be kept for any 

 length of time, the paper should be varnished over with sandarac varnish. A 

 small quantity of balsam of Peru may be added to perfume the mixture, so as to 

 cause its combustion to be attended with a pleasant odour. The greenish 

 coloured very porous mass, which assumes the serpent shape, is a mixture of 

 carbonate of potassa, oxide of chromium, carbon, and a small quantity of 

 neutral chromate of potassa. The author states that this mass is an excellent 

 substance for polishing all kinds of metals. The mixture above specified should 

 be kept in a dark place. 



Dr. Grager has proposed a new method for the reduction of chloride of silver 

 dissolved in ammonia by means of metallic zinc. This process, according to 

 the author, succeeds very well, and yields a silver of greater purity than is ob- 

 tained by the process for reduction of silver by the moist way now in use, pro- 

 vided the operation be carried on in closed bottles. The silver, after complete re- 

 duction, is first thoroughly washed with concentrated hydrochloric acid, next with 

 water, and, lastly, for some moments with dilute ammonia, and then again 

 with distilled water. It is clear that this method of reduction involves the use 

 of a considerable quantity of ammonia ; but this, the author states, can in great 

 measure be recovered by distillation. 



A mode of distinguishing the deposit of arsenic obtained by Reinsch's pro- 

 cess from salts of mercury has been published by Mr. James St. Clair Gray. 

 It is for mercury a test of even greater delicacy than that afforded by sublima- 

 tion of metallic globules from the coated copper foil, and is possessed also of 

 the advantage that the result can be seen by the unaided vision, while its ap- 

 plication is extremely simple. It is founded on the great affinity which exists 

 between mercury and gold. One of the copper slips, coated in the ordinary 

 manner by Reinsch's process, is first washed in pure distilled water and then 

 thoroughly dried ; when thus prepared it is rubbed with a flattened bead of pure 

 gold, or, should this not be at hand, a flat signet ring will suffice. The result, 

 if the coating be mercurial, is that a portion of the mercury, whose affinity for 

 gold is greater than for copper, is transferred from the copper to the gold, ap- 

 pearing on its surface as a clear, white, shining, metallic crust, this being more 

 conspicuous the more highly coloured the surrounding gold is. The stain is at 

 once removed by pure strong nitric acid. This is of itself perfectly conclusive 



