SOLDERING METALS. 55 



a tube similar to that of Regnault's hygrometer with some mercury 

 at the bottom. Fig. 31 represents a tube arranged for this 

 purpose, the liquid being sulphur dioxide (the 

 gas produced on burning brimstone), which at 

 ordinary warm temperatures is a gas, but con- 

 denses to a liquid on chilling below 0. The 

 lowest obtainable temperatures produced by 

 the most powerful frigorific agents are obtained 

 in somewhat similar fashions (Chapter XXI.). 

 Expt. 47. To Solder Tin and other Metals 

 together. The tap mentioned in the last 

 experiment is fixed to the tin can by boring a 

 hole in the latter, applying the tap in position 

 thereto, and then cementing the two together 

 by means of a little melted solder held by a 

 Fig. 31. Tube Ar- not tool usua u y called a "soldering iron," al- 

 rangement for freez- ,, , ., . J n , ,. 6 n ' 



ing Mercury. though it is really made of a lump of copper 



riveted to an iron bar to support it, and pro- 

 vided with a wooden handle. The construction of home-made 

 apparatus of metal is greatly facilitated by knowing how to use 

 this soldering tool; the chief points to notice are that all the 

 surfaces to be soldered must be clean and bright; if dirty or 

 rusty they must be filed or scraped bright. The "tongue" of 

 the soldering tool (the copper "bit") must not be heated too 

 strongly ; if this should occur the solder adhering to it will 

 probably be burnt off it and it will not then take up any more 

 melted solder ; the tip should then be filed whilst hot, dipped for 

 a moment in a solution of chloride of zinc, got by dissolving a 

 fragment of zinc in a teaspoonful of hydrochloric acid (whereby 

 hydrogen gas is copiously evolved, Expt. 13), and then applied to 

 a strip of solder ; a little of this melts and sticks to the hot copper, 

 wetting it with melted solder just as a cold lump of copper would 

 be wetted with water if dipped therein. It generally facilitates 

 the sticking of the solder to the scraped surfaces to be stuck 

 together if they are brushed over with this chloride of zinc solution 

 just before applying the tool ; powdered resin or salammoniac is 

 sometimes used instead of chloride of zinc solution with the same 

 results. 



To make a neat join with a soldering tool requires some practice 

 and dexterity, but a little patience will soon enable you to manage 

 the tool sufficiently well to make a serviceable, if not a very 

 elegant, connection. The tool is usually heated in an ordinary 

 fire, taking care not to make it quite red hot ; a very convenient 

 wav of heating a small-sized tool is to support it on a tripod or 



