Vol. XXII. No. 3.] 



POPULAE SOIEI^CE I^EWS. 



37 



JPratttcal CJjemtBtrp anU t!)e 3lrU(. 



A ROTART THERMOMETER. 



This ingenious instrument is described in 

 La Nature, and is the invention of M. 

 Rabinovitch. It is quite sensitive to small 

 changes of temperature, and, if desired, regis- 

 ters the highest and lowest points reached in 

 a given time, or draws automatically a curve 

 on a sheet of paper, showing all the varia- 

 tions. It will also sound an electric bell when 

 an\- desired temperature is attained. 



The general appearance of the instrument 

 is shown in Fig. 1, and the details of its very 



Fio. 1. 



simple mechanism in Fig. 2. The main reser- 

 voir or bulb, a, is filled with alcohol ; while the 

 curved tube, 66', into which it is drawn out, 

 contains mercurj'. As the temperature rises, 

 the alcohol expands, forcing the mercury 

 along in the tube, and so changing the centre 

 of gravity as to cause the whole to revolve 

 on the central pivot, c, to which it is attached. 

 The metallic index, A, which is placed at the 

 end of the tube, thus indicates on the scale, ti, 

 every variation of temperature. 



Two extra pointers, d and e, are pushed in 

 either direction by the revolving tube, and 



Fio. 2. 



indicate the highest and lowest points reached 

 in anj' given time. At fc there is an electric 

 connection, which can be moved along the 

 scale, and is completed by the metallic 

 pointer, A, causing a bell to ring at any tem- 

 perature to which it may be set. At m a 

 piece of metal, carrying a pencil, n, is at- 

 tached to the tube ; and if a sheet of paper, 



moved by clockwork, is made to pass before 

 it, a tracing will be made which will show all 

 the variations of temperature during any given 

 time. 



The simplicity and cheapness of this instru- 

 ment are also among its most important 

 advantages ; and, if placed upon the market, 

 it would doubtless find a ready sale. 



A SIMPLE METHOD OF ILLUSTRATING 

 CHEMICAL EQUIVALENTS. 



Professor Torrey, in a recent number of the 

 American Chemical Journal, describes a simple 

 method for showing to students in elementary 

 chemistry the difference in the atomic weights of 

 different metals, and determining these weights 

 with approximate accuracy. He writes : — 



" While the freshman clas.s were studying the 

 action of hydrochloric acid on metals, it was 

 noticed by some of them that some metals ap- 

 parently liberated more hydrogen than others. 

 This observation aroused considerable interest, 

 and I thought it would be well to introduce the 

 equivalent then and there. 



'' The question was put as follows : What weight 

 of each metal icill it lake to liberate one milligram of 

 hydrogen f 



" The metals chosen for experiment were iron, 

 zinc, and aluminium. The apparatus given to 

 each student consisted of a three-inch evaporating 

 dish and a common six-inch test-tube. In some 

 cases graduated gas-tubes were given out. Fifty 

 to a hundred milligrams of the metal having been 

 accurately weighed, the test-tube was filled with 

 acid (in most cases hydrochloric acid), and in- 

 verted in the evaporating dish, previously one-third 

 filled with the same acid. The piece of metal was 

 now quickly brought under the tube, and the whole 

 apparatus left to itself till the solution was com- 

 plete. Sometimes a gentle heat was applied. Later 

 on, it was found better to put the metal ia a little 

 cup (made by cutting off a half -inch from the 

 lower end of a small test-tube) before bringing it 

 under the tube, thus avoiding the possibility of 

 bubbles being carried out by the descending cur- 

 rent of acid. When solution was complete, the 

 tube was transferred to a large jar of water, and 

 the acid displaced by water. It was then cooled 

 to the temperature of the room. 



" When graduated tubes had been employed, the 

 volume could then be read directly, the necessary 

 corrections for temperature and pressure made, 

 and the equivalent deduced. When ordinary test- 

 tubes had been employed, the line where gas ended 

 and water began was marked on the tube by tying 

 a piece of fine thread round it. Water was then 

 run in from a carefully graduated burette, till the 

 space previously occupied by gas was occupied by 

 water. The volume thus obtained represented the 

 volume of gas obtained, and was corrected for 

 temperature and pressure as usual. 



" I acknowledge the apparent crudeness and 

 roughness of the process, but invite attention to 

 the following results : — 



" It should be said that the level of the water in 

 the tube was always brought to the level of the 

 water in the jar before reading the volume, and 

 that the tube was left standing long enough to get 

 to the temperature of the room after being placed 

 in position." 



A GELATINE BATTERY. 

 A GELATINE cell has been designed for use in 

 situations where it is desirable to have a battery 

 which shall be able to withstand violent shaking 

 and jarring without deterioration. There are 

 several points of interest in the process of manu- 

 facture of this cell, which has been patented. The 

 gelatine is prepared by soaking Irish moss, or other 

 sea moss, in cold water until it becomes softened 

 by absorption, and allowing it to soak until the 

 starchy matter of the plant begins to ferment or 

 sour. When it reaches this stage, a quantity of water 

 about equal in bulk to the soaked moss is added, and 

 the whole boiled for from fifteen to thirty min- 

 utes. The amount of water may, however, vary 

 according to the desired consistency of the final 

 product. After the boiling, a quantity of sal- 

 ammoniac or other salt of an alkali is added, 

 sufficient to make the excitant a good electro- 

 lytic conductor, and to assist in the exciting 

 action in the zinc, and the mass is then subjected 

 to further boiling. These repeated boilings serve 

 to completely rupture all the starch-cells of the 

 plant, and dissolve the gluten, while the fer- 

 mentation probably assists in decomposing the 

 cellulose. The material then becomes of a uni- 

 form pasty consistency, and the sal-ammoniac is 

 thoroughly incorporated and dissolved throughout 

 the mass. The latter is poured into a receiving- 

 vessel, and a small quantity of bisulphate of mer- 

 cury is added. The latter improves the electro- 

 lyte by slightly acidulating the same, and keeps 

 the zinc amalgamated. The mass is then allowed 

 to cool, when it is packed in the battery jar 

 between and around the electrodes. It becomes 

 of a comparatively stiff, pasty consistency, and 

 preserves the electrodes in place, however much 

 jarring the battery may be subjected to. The 

 inventor states that this electrolyte resists low 

 temperatures, and that during use more or less 

 fermentation goes on, preserving the acidulation. 

 and tending to raise the electro-motive force. — 

 Mechanical World. 



MODERN EXPLOSIVES. 



The composition of some of the modern high 

 explosives, according to Engineering, is as fol- 

 lows : — 



Dynamite : 75 parts of nitro-glycerine and 25 

 of infusorial earth. 



Dualine : 80 parts nitro-glycerine and 20 of nitro- 

 cellulose or gun-cotton. 



Rendrock : 40 parts nitro-glycerine, 40 of nitrate 

 of potash or soda, 13 of cellulose, and 7 of paraf- 

 fine. 



Giant Powder : 36 parts of nitro-glycerine, 48 of 

 nitrate of potash or soda, 8 of sulphur, and 8 of 

 resin or charcoal. 



Mica Poioder: 52 parts nitro-glycerine and 48 of 

 pulverized mica. 



Tonile : 52^ parts of gun-cotton and 47J of 

 nitrate of baryta. 



Blasting Gelatine : 92 parts of nitro-glycerine and 

 8 of gun-cotton. 



Atlas Powder: 75 parts of nitro-glycerine, 21 

 of wood-fibre, 2 of carbonate of magnesia, and 2 

 of nitrate of soda. 



Rackarock: 77.7 parts of chlorate of potash, and 

 22.3 of nitro-benzol. 



It will be noticed that nearly all the above ex- 

 plosives are composed principally of nitro-glycerine ; 

 and it is probable that in most cases the other in- 

 gredients only act as absorbents of this liquid, and 

 really add nothing to the explosive power. The 

 decomposition of nitro-glycerine is practically in- 

 stantaneous, and the slower-acting nitrates and 

 hydrocarbons must be left far behind when the 



