550 



Progress in Science. 



[Oaober, 



oxalic acid, after which these materials may be heated even up to their point 

 of fusion without exploding. 



At a comparatively remote period, saltpetre was regularly manufactured in 

 most European countries by a process too long to be further alluded to here, 

 and well known, undoubtedly, to most of our readers. MM. Thiercelin and 

 Willm state that the richness of the saltpetre-yielding materials recently tested 

 by them varies very much. They found that the efflorescence now and then 

 met with, especially on the walls of old stables, contained as much as 67 per 

 cent of saltpetre ; but this material is rare. Old wood-ash yielded £ per 

 cent; the mortar of a wall covered with ivy yielded 2*6 per cent; and 

 the mortar of the same wall at a spot not covered with that plant, 4-6 per cent 

 of saltpetre. 



CHEMICAL SCIENCE. 



The following test for the detection of small quantities of sulphur present in 

 coal-gas has been proposed by Dr. V. Wartha. Form first before the blow- 

 pipe, in the loop of a platinum wire, a bead of pure soda, and next pass this 

 bead over the edge of the gas flame, after which the bead is held in the interior 

 of the flame in order to deoxidise the sulphates and sulphites of soda into sul- 

 phuret of sodium; the bead is then transferred to a porcelain basin, crushed, 

 and some nitro-prusside of sodium added, whereby the smallest trace of 

 sulphur will be detected. This Jrea&ion is fifty times more sensitive than that 

 upon silver-foil; and the test can be performed in about three minutes, whereas 

 Dr. Vogel's sulphur-copper reaction for this purpose takes four hours. 



The idea of using a cone made of very porous eathenware, and as a substitute 

 for the paper filter, has been carried out by Mr. C. E. Munroe in the following 

 manner : — The cones are made of very light, porous earthenware, and have an 

 angle of about 6o°. They are used in the following way : — A se&ion of a 



seamless rubber tube, a, is 

 Fig. 18. stretched around the mouth 



of a funnel, b, preferably a 

 Bunsen funnel, allowing a 

 portion of the tube to project 

 above the top. This part will 

 immediately arrange itself at 

 right angles to the top of the 

 funnel; into the circle thus 

 formed the cone, c, is put. It 

 is then connected with the 

 Bunsen pump. When the 

 cone is moistened and the 

 pressure applied, the rubber 

 band forms an air-tight joint, 

 and the liquid runs through 

 with great rapidity. Before 

 the cones are applied to quan- 

 titative work they must be 

 carefullywashed,firstwith con- 

 centrated hydrochloric acid, 

 then with distilled water,dried, 

 and weighed. A small por- 

 celain crucible is kept at the 

 balance in which to weigh 

 them. The cones can be 

 used repeatedly, and can re- 

 place paper filters in every 

 case. They will, undoubtedly, 

 be found to be of great value 

 in commercial work, for drying crystals and filtering corrosive liquids. As 

 they will stand sudden changes of temperature without breaking, they can be 

 substituted to advantage in many cases for crucibles. 



