TRANSACTIONS OF THE SECTIONS. 35 



dred to india-rubber and gutta percba ; it can be produced of any colour or shape, 

 and can be manipulated in almost every conceivable manner. The basis of the 

 material Parkesine is gun-cotton, but a variety of other materials are used. These 

 materials were exhibited : they consisted of various solvents, cotton waste, oils, &c. 

 Various articles, manufactured from Parkesine, were shown, and its various appli- 

 cations thus proved. A cotton which is not readily explosive, is desirable in the 

 manufacture ; iodide and chloride of zinc being used to prevent the rapid combus- 

 tion of the cotton. Mr. Parkes's solvent is suitable for the solution of india-rubber, 

 gutta percha, and various gums ; and bj r mixing these substances in various pro- 

 portions, the different varieties of Parkesine are made. The author then referred 

 to the value of Parkesine as an insulating material for telegraphic purposes, con- 

 sidering it far superior to india-rubber and gutta-percha, or to any combination of 

 materials hitherto used. The strength of the material is considerable, a cable of it 

 being capable of supporting one mile in length of its own substance, whilst sound 

 joints can be made with the greatest facility. 



On the Action of the Alkali Metals in determining the Explosion of Gun-Cotton. 

 By Wbntwokth L. Scott, F.C.S., F.A.S.L., 4'c 

 The author stated that in the course of some experiments he accidentally dropped 

 a piece of potassium on some gun-cotton ; the gun-cotton immediately exploded. 

 He tben instituted a series of experiments, to ascertain what conditions were essen- 

 tial for explosion to take place, whether the explosion was due to moisture, whether 

 other metals would act similarly on the gun-cotton, &c. He found that by taking 

 precautions to prevent friction, the gun-cotton still exploded. When sodium was 

 used a like result was obtained, even though the gim-cotton was rendered perfectly 

 anhydrous. If an amalgam of potassium or sodium was used no result was obtained. 

 Various metals were tried, but decided effects were obtained only with the metals 

 of the alkalies, although finely-divided metallic arsenic has the property of increa- 

 sing the explosive powers of gun-cotton, the mixture readily exploding on percus- 

 sion, and the author thought the same might be usefully applied. 



On a Method of estimating Carbonic Acid in the Air. 

 By Dr. An t gtjs Smith, F.B.S. 



The author explained a mode of analysis which he has called minimetric. The 

 idea, he said, might perhaps not be quite new, but it is well to give the method a 

 name. It is based mainly on the fact that we can retain in the memory with great 

 exactness the character of a precipitate of a given degree of translucency. For 

 carbonic acid, the author finds a precipitate of carbonate of baryta, formed in half 

 an ounce of baryta-water by 0-2515 cub. centim. of carbonic acid, or by nearly three 

 times that amount in lime-water, to be most easily remembered. If the carbonic 

 arid in air is sought, the air is made to act on the baryta- water until the desired 

 precipitate is obtained. In other words, we use the smallest measure of air which 

 will produce the precipitate. For this reason the name mvnirmetric is adopted. The 

 method may also be used for hydrochloric acid, sulphuric and sulphurous acids, 

 sulphuretted hydrogen, &c, and probably has been used frequently without being 

 brought forward as a method for accurate use. 



Two ways of using this method of analysis were described. The first was by the 

 use of a finger pump, an elastic ball with two valves, connected with a bottle con- 

 taining baryta-water. On pressing the ball the air in it is driven out, and on re- 

 moving the pressure-air is drawn in through the liquid. The air and liquid are 

 then shaken together, and the operation repeated until the precipitate is obtained. 

 For ordinary use a ball to contain two ounces is found most suitable ; the bottle 

 should have the same capacity as the ball + the space required for the liquid, so 

 that the air contained in the bottle at the commencement of the experiment may 

 coimt as one ballfull. 



A Table is constructed like the following, but of course it must be adapted to 

 the size of the ball. 



3* 



