SOLDERING 491 



made near the middle of tlie longer piece by cutting into 

 the side of the tube with the round file, while one end of 

 the short piece is cut in circularly to fit over the opening 

 in the longer piece. These pieces are fitted together and 

 then fastened down to a small block of wood by a few small 

 nails. The joint is then heated fairly hot (to remove grease, 

 etc.) with the flame and then a few drops of the acid are 

 applied to the joint. This acid is at once vaporized by the 

 heated metal but in this process the acid penetrates every 

 portion of the joint. The flame is now reapplied and at th^ 

 same time the end of a piece of wire solder (string solder) is 

 placed on the joint. The solder melts quickly and runs into 

 every part of the joint. Beginners usually get on too 

 much solder. Only a small amount is needed as a rule 

 and more may even do harm. The flame can be directed 

 beneath the tube to insure soldering of the lower part of 

 the joint. More acid can be applied if the solder does not 

 stick at the first application. As soon as the joint is seen 

 to be run full of solder the flame is removed and no more 

 solder is applied. Cold water is poured over the tubes and 

 the soldering is complete. The cannula is now removed 

 from the board and a fine rasp or wood file (not a fine file 

 for metal) is used to file away any excess lumps of solder 

 and make the joint smooth and regular. 



This operation is typical for most of the soldering re- 

 quired in the laboratory. But a further complication arises 

 if two pieces are to be soldered together close to a joint 

 which has already been soldered. In this case heat from 

 the flame may melt apart the first joint while the solder is 

 being applied to the second. This can usually be avoided 

 by wrapping the first joint with wet cotton or a wet cloth 

 (probably tied on with soft copper wire) while the second 

 joint is soldered. 



The making of oncometers for the kidney, spleen or in- 

 testinal loop, etc., can be readily done by simply cutting 

 out pieces of sheet brass into the proper shape and then 



