Journal of Agriculture. [8 Jan., 1907. 



A good driver will always have the water and steam as near tO' oqe point 

 as possible. 



Blow-off Cock. — In "blowing down" a boiler, the blow-off cock 

 should always be turned backward and forward two or three times before 

 it is fully opened. This prevents it from sticking, as it might do if 

 opened " full " at once. 



Cleansing and Testing Boilers. — Every boiler should be carefully 

 examined inside and outside whene\er it is cleansed, and it should be 

 tested by hydraulic pressure once in each twelve months, to not less than 

 50 per cent, above the pressure at which the safety valve blows off. In 

 doubtful cases, boilers should be subjected to a test of double the pressure 

 at which the safety valve blows off. The best means we have of ascertain- 

 ing the safety of a boiler with any degree of certainty, is by applying 

 pressure, for even if a boiler be well proportioned, and be made of the best 

 material, there is always the possibility of the existence of defects, such as 

 bad welding or riveting, plates having been burned in flanging, or cracked 

 in bending, or the plates may have been badly punched, and when put to- 

 gether the iron is either cut away so as to bring the holes fair to one an- 

 other, or the plate is strained by a drift having been driven in the holes to 

 allows the rivets to enter. The rivets may be little, if any, more than half 

 their proper size where the plates join. After a boiler has been riveted 

 the defects I have mentioned can onlv be detected by a hydraulic pressure 

 test. Some years ago I saw in a boilermaker's yard a boiler, all punched 

 and plated, and ready for riveting — nearly all the l]oles were half-holes. 

 After the boiler was finished it was tested, and at a pressure of only 70 

 lbs. per square inch the flue came down. I have seen the gusset stays put 

 in between the double angle irons on the front and the shell with the iron 

 nearly all cut away between the holes and the edge of the plate. These 

 defects could, as I have stated, only be discovered by testing. When the 

 construction of a boiler will allow\ it should always be examined and 

 sounded with a hammer before the hydraulic test is applied. All boilers 

 should be thoroughly examined and tested before they are built in position, 

 and I may mention that a hydraulic test and a steam test are equal in 

 pressure and, strain on a boiler. Boilers could, however, be constructed 

 which would stand a greater pressure of water than ofi steam. If a boiler 

 has been resting on damp walls, especially where the dampness results from 

 the use of mineral water, the parts where the boiler has been so resting are 

 often corroded, and the boiler should be carefully examined there. I have 

 seen the plates of a boiler reduced to less than one half-their original thick- 

 ness, owing to the cause mentioned, while the remaining part of the boiler 

 was in good condition. The chief cause of explosions is the unsafe con- 

 dition of boilers through age, corrosion, wasting, &c. , which necessitates 

 undue working pressure. There are now at work in this State many 

 boilers which have been in use for over 20 years. Some of these boilers 

 have been at work at different places, and have been fed with different 

 waters, and extra care and caution are required in working, examining, and 

 testing them. 



Strain upon a Boiler. — To show^ the amount of strain upon a high- 

 pressure boiler 26 feet long. 6 ft. 6 in. diameter, 3 ft. 6 in. flue, 

 working at a pressure of 50 lbs. per square inch, or 7,200 lbs. per squaie 

 foot, we have only to multiply the number of square feet of surface exposed 

 to pressure, namely. 863 feet, by 7,200, and we find that a boiler of the 

 dimensions I have given has to sustain a force of 2,773 tons. This calcu 



