84 ANNUAL OF SCIENTIFIC DISCOVERY. 



connection with the mines and the earth by means of these screws, to 

 turn this handle as rapidly as possible, and to depress this key when the 

 signal to fire is given. It will, I believe, be evident to all present that 

 this system is very greatly to be preferred to the plan of exploding 

 mines by voltaic agency. 



Before quitting this subject I must just allude to the successful 

 application which has been made of vulcanized India-rubber to the 

 preparation of receptacles for the powder-charges employed in sub- 

 marine operations. Such bags are perfectly water-tight under very 

 considerable pressure ; they are far more easily transportable and gen- 

 erally manageable than the wooden or metal vessels which have hith- 

 erto been employed for the reception of powder to be exploded under 

 water. 



The following plan for protecting wooden camp-huts from fire has 

 been found efficient in the British service : It consists in coating the 

 wood with a species of artificial stone (a double silicate of lime and 

 soda), readily produced by applying alternately a solution of soluble 

 glass and lime-wash to the surface of the wood. This coating has been 

 found to offer very great resistance to fire, and to be very durable 

 when exposed to the effects of rain and cold. Attempts have been 

 quite recently made to afford a similarly permanent protection to tents, 

 by the employment of silicate in some form, which have led to the dis- 

 covery of a simple process whereby canvas may be thoroughly im- 

 pregnated with an insoluble silicate, which protects it to a remarkable 

 extent from fire. 



The regular supply of drinkable and icliolesome water to troops at 

 foreign coast-stations, and in positions temporarily occupied in time 

 of war, has on many occasions been attended with formidable diffi- 

 culties, which in some cases have been met by the employment, in 

 such localities, of the apparatus introduced by the late Sir Thomas 

 Grant, for the production of fresh water, on board ship, from sea- 

 water, and which has, for some time past, been extensively used in 

 the navy. The apparatus simply consists of an efficient condenser, 

 whereby distilled water is produced from the steam generated in the 

 ship's or other boilers. The product, which exactly resembles ordi- 

 nary distilled water, though drinkable, is by no means pleasant, when 

 first obtained ; it is entirely wanting in the briskness more or less 

 common to all fresh water, and which is due to the gaseous matter 

 contained in solution. If this water be, however, kept in partially 

 filled tanks for some time, and particularly if by the motion of a ves- 

 sel, for example, it be maintained in continual or frequent agitation, 

 it becomes partly aerated, and is thus rendered somewhat more pala- 

 table. It always possesses, however, the peculiar unpleasant flavor of 

 distilled water which has been produced from steam generated in 

 metal vessels, and which is due to the presence, in solution, of 

 minute quantities of empyreumatic matter resulting from the decom- 

 position of organic substances contained in the water. This flavor 

 may be at once removed by passing the aerated water through a ves- 

 sel containing charcoal, which absorbs the minute quantities of organic 

 matter, and promotes their rapid oxidation by the oxygen dissolved in 

 the water. 



