Progress of Invention. 227 



ordinary barrels from leakage when filled with certain liquids, and 

 this imperfection very often, as for example in the case of the petro- 

 leum and coal oils, is not unattended with danger. Barrels are now 

 formed in the oil districts of America which are free from all imper- 

 fections of this kind ; while, at the same time, they are light, strong, 

 and inexpensive. They are formed by wrapping spirally round a 

 mould, representing the interior of the intended barrel, strips of 

 white oak, and crossing them with other slips, that are attached to 

 them by a glue which is adapted to the purpose. This process is 

 repeated until the requisite strength and thickness are attained, 

 which, in ordinary cases, is when there are twelve or fourteen layers 

 thus crossing and attached to each other. The heads are formed in 

 a similar way, and are firmly united to the bodies. 



Step for Shafting. — A serious mechanical difficulty is expe- 

 rienced on account of the great pressure which is sometimes exerted 

 against the step in which an upright shaft revolves. The friction 

 produced, and the heat by consequence developed, has often led to 

 the welding together, or the fusion of the metals, notwithstanding the 

 attention paid to lubrication. This inconvenience exists whenever a 

 thrust is exerted by the shaft, in whatever direction that thrust may 

 be, whether upwards, downwards, or laterally ; and hence great 

 difficulty has arisen in making suitable provision for resisting the 

 thrust of the screw shaft, where, by acting within the vessel, it gives 

 rise to propulsions. Many contrivances have been proposed, and 

 several have been used to meet the difficulty. A recent, and appa- 

 rently a very effective, invention, intended for this purpose, consists 

 in making the end of the shaft play against chilled iron balls 

 placed in a cup-shaped receptacle. The end of the shaft is so formed 

 that it acts on the balls at an angle of 45°, and presses them against 

 the rim of the chamber which contains them ; and it is so arranged, 

 that the difference between the diameter of the circle they traverse 

 and the rim is such as to give rise to a uniform rotation, and there- 

 fore to a uniform wear and tear. This contrivance appears particu- 

 larly well adapted to the steps of turbines, which, when the column 

 of water is high from the great pressure sustained and the enormous 

 velocity of rotation, present very great difficulties in this respect. 

 To a certain extent, indeed, the impossibility hitherto of obtaining 

 a suitable step has set limits to the height of the column of water 

 that may be utilized by them. Should this contrivance be found to 

 answer, as the rubbing is changed into a rolling friction, the difficulty 

 will be entirely got rid of. 



Preservative Coatings for Metals. — One of the most effective 

 modes of preserving the common metals consists in coating them 

 with a thin film of gold or platinum. This, however, is attended 

 with expense and trouble ; and the same object may be as well, if not 

 better, attained by coating with oxides. For this purpose, however, 

 it is indispensable that the oxides should be made to adhere with 

 great tenacity, a circumstance which long prevented the preservative 

 qualities of oxides being fully utilized. The oxides of iron and lead 

 are the most suited for preservative coatings, especially as they are 

 capable of sustaining, without change, a very elevated temperature. 



