162 Wisconsin Academy of Sciences, Arts, and Letter's. 



down gradually, and in shape like the bottom of a wash-bowl, 

 becoming thinner at the lowest point until finally breaking open, 

 it left rough, ragged edges and a hole about eight inches in diame- 

 ter. The whole weight of three and a half tons was raised about 

 thirty feet and thrown over back, striking the ground at an 

 angle of about thirty degrees, and sliding along, tore off every 

 particle of the engine. 



These deposits in boilers are the most difficult matters steam 

 users have to contend with, but its formation to a dangerous thick- 

 ness can be prevented by frequent cleaning out, also by frequentlv 

 letting out a little water through the day when the boiler is under 

 pressure. It is a bad practice, and, of course, a common one, to 

 let the water all blow out of the boiler, after the fires are out and 

 before sufficiently cooled. The heat retained in the metal and 



Fig. 7. 



surrounding walls will cause the deposit to bake to the iron so 

 that nothing less than a hammer and chisel will remove it. Care 

 should be exercised in setting boilers so that they may be examined 

 at different times, and to keep them in places as dry as possible. 

 Iron wastes away fast enough at best, and if leaks occur where 

 the boiler is in contact with brick and mortar, corrosion goes on 

 so rapidly that the best boilers may be rendered unsafe in a year 

 or two. When leaks are discovered they should be considered 

 signs of wearing out, and should receive attention at once. Usu- 

 ally, however, because it is small or does not let out the water faster 

 than it can be replaced, it is allowed to go. It is treading on a 

 dangerous path. 



