64 Laboratory Arts 



ammonium chloride to animal refuse, but clean water appears 

 to be as suitable as any \ save perhaps in the case of 

 dies for stamping metal, punches for metal, etc., which may 

 be finally quenched in oil (the kind does not appear to matter 

 much). Oil, having a high boiling point, continues in contact 

 with the metal till quite cold, whereas water is converted into 

 steam near the hot object, which is thus surrounded by 

 a steam jacket and cools more slowly. The main object 

 of the addition of sulphuric acid, salt, salammoniac, etc., to 

 the quenching water, appears to be that of raising its boiling 

 point. 



The following list of temperatures suitable for tempering 

 steel articles will be useful 



220 C., pale straw dies, punches, taps, glass or china 

 drills, needles, lancets, small drills, cold steel chisels. 



245 C., dark yellow razors, scalpels, twist drills. 



250 C., dark straw penknives, wood drills. 



2 5 5 C., clay yellow chisels and shears, centre punches. 



260 C., brown yellow plane irons. 



270 C., very pale purple table knives, arbors, pins. 



2 7 5 C., light purple watch springs. 



290 C., dark purple softer springs. 



310 C., dark blue fine saws. 



320 C., pale blue large saws. 



330 C., greenish blue tools of very mild temper. 



As lead melts about 335 C., it will be seen that after 

 hardening, steel may be given a very mild temper by being 

 immersed in melted lead, and quenched in water. 



Uses of Studs. The word " stud " is applied to a steel 

 rod having threads in opposite directions cut from each end, 

 separated by an unthreaded portion. It is screwed into a solid 

 up to the point where the threads cease, then plates or other 

 portions of mechanism may be bolted to the solid by means of 

 a washer and nut travelling the projecting thread. 



Studs are made by screwing first one end and then the other 

 of a short rod (previously measured to suit its purpose), the 

 space between the two threads being determined by the thick- 

 ness of the material to be bolted to the solid. 



