Steam Boiler: Small Brass Shell Boiler, Screwed and Soldered (Hopkins, Model Engines and Small Boats, 1898)

A small steam boiler for model engines and boats: a brass cylinder 4 in across, closed by two brass heads tied together by a brass stay rod, its seam held by two rows of brass screws and sealed with solder. It sits in a russia-iron jacket over an alcohol lamp, with a weighted safety valve and fusible plugs that put the lamp out if the water runs low. Result: a strong little shell boiler, 6 to 12 in long to suit the engine. Source: N. M. Hopkins, Model Engines and Small Boats (1898), ch. III. Unknown: the working pressure and the valve's sizes. Picture: the book's Fig. 33.