loO Transactions. 



of engine. By mechanical means its action can be greatly retarded and kept 

 within safe limits, but I do not think there is at present any known remedy 

 for its perfect prevention. 



In using surface condensers the same water is being continually converted 

 into stea.m and reconverted into water. Has this anvthino- to do with liffcinor 

 the water above its true level ? Is there a large, or any, portion of the air 

 extracted with this continual distillation ? 



Secondly. — The effect of using surface condensed water and high-pressure 

 steam in the boiler is to destroy the plates of the boiler, either by galvanic 

 action or from some electrical influence. I am inclined to believe more in the 

 former because we have the brass tubes of the condenser and the copper pipes 

 forming the negative pole, and the boiler and hot well forming the positive 

 pole, the sea water circulating in the condenser and nsed to supplement the 

 feed, forming a saline solution as a medium. On leaving out the zinc plates 

 for a few trips, streaks of black oxide of iron were discovered about the 

 superheater, and other parts in the boiler, especially where the greatest heat 

 was. The superheater was cleaned and painted, and zinc plates replaced in 

 the water space of the boiler. Since then no injurious effects have taken 

 place. 



Another strange phenomenon is the deposition of a calcareous substance 

 thrown against the top of the shell of the boiler as if one were to take 

 a handful of mortar and throw it against the wall, but these deposits only 

 require removing about once in two m.onths. Since leaving off the use of 

 tallow for lubricating the cylinders these deposits on the upper part of the 

 shell are scarcely noticeable. 



I must not forget to mention another important matter in reference to the 

 preservation of the boiler, especially where exposed to the action of the steam, 

 viz., — the application of Portland cement, put on in the same way as white- 

 wash ; it is the best preservative that I am acquainted with, and I am 

 indebted to Mr. James Stewart, C.E., for this hint. 



In conclusion I may state that some persons imagine that' compound 

 engines are complicated. This is not so ; neither is there any difiSculty in 

 starting or stopping them. When we find boats of 3,000 tons steaming 10 

 knots on a consumption of 18 tons per 24 hours it speaks well for this class 

 of engine. The " Adriatic," the largest steamer afloat next to the " Great 

 Eastern," has compound engines, and has just diade the quickest trip across 

 the Atlantic on record. There is nothing whatever to prevent any of the 

 steamers running on the New Zealand coast from being compounded, with 

 results equal to those here stated, and it is also satisfactory to know that 

 there are special facilities for converting them in Auckland. 



