WAX EXTRACTORS. 139 



made. It may be necessary to give a rule for 

 cutting out the material for making hollow cylin- 

 ders such as this : Multiply the diameter by 3-f , 

 and add what is required to make the joint. If a 

 plain overlapping joint is used, add the amount of 

 lap ; but if a hooked joint is used, three times the 

 length of the turned over parts should be added, 

 usually about f in. In the present case, a strip 

 of perforated tinplate, 29 J in. by 7| in., will form 



<\ 



Fig. 131. Pattern for Cylindrical Top of Boiler. 



the cylinder, the extra width being f in. for the 

 wiring on top, and 3 in. to make the joint at the 

 bottom. 



The conical bottom of the basket has the same 

 slope as that of the steamer ; the same pattern 

 will do for both, except that the radius of the 

 basket pattern may be f in. less. A perforated 

 tinplate tube, similar to that in the steamer, but 

 i in. larger, is fixed in the centre of the comb 

 basket ; but, while the tube in the steamer is open 



