68 Mr. Robb on a new Portable SmitJCs Forge. 



The Society proceeded to the annual election of Office-bearers, and the 

 vote papers baring been collected, Mr. Dawson and Mr. Cockey were 

 appointed to examine the votes and report the result, and they retired 

 for this purpose to another apartment. During their absence, 



Mr. Charles Robb, civdl engineer, read a paper explanatory of the 

 principle of a new Portable Smith's Forge, Furnace, and Ventilating 

 Apparatus, the invention of Mr. Chaplin, of Glasgow. Models of the 

 machine were exhibited by Mr. Robb, showing its mode of operation. It 

 is constructed wboUy of iron, and may be folded up into the dimensions 

 of three feet six inches, by two feet six inches, with eight inches of thick- 

 ness. It is contained in an upright frame, and consists of an eccentric 

 fan with three blades, which is set in motion by means of a crank handle. 

 In the model exhibited, the ratio of the diameter of the driving wheel to 

 that of the pulley on the fan spindle, was twenty to one. A hundred 

 revolutions of the driving wheel per minute is a rate of motion that can 

 with all ease be produced and sustained for a long period ; and this would 

 give a velocity of 2000 revolutions of the fan per minute, or a speed of 

 5750 feet at the circumference of the fan. To the upright frame, the 

 receptacle for the fuel, which is simply an iron tray, mounted on wheels, 

 for shifting, is attached by bolts, and to the end of this the cold water 

 trough is affixed. A dead plate is also placed before the inner front of 

 the frame, the design being thus to protect the blowing mechanism from 

 the injurious influence of the heat. The main cause stated by Mr. Robb 

 for the extraordinary efficiency of the machine, viewed in proportion to 

 the slight power required for its impulsion, was the extreme lightness of 

 the various parts of the fan, together with the accuracy and delicacy of 

 their motion. In commenting upon its superiority to the common smith's 

 forge, Mr. Robb claimed for it not only the qualifications of greater com- 

 pactness and durability, (its titles to which are indisputable,) but also that 

 of greater efficiency. As illustrative of its rate of heating, he referred to 

 the experiments made with it in the blacksmith's shop at the Woolwich 

 Dockyard, in the presence of the chief engineer and master shipwright. It 

 was found then that a bar of iron, \\ inch in diameter, could be brought 

 to a welding heat in from three to four minutes. By a slight modifica- 

 tion, involving merely the addition of a set of fire bars, through which 

 the blast is directed, the instrument was also capable of being converted 

 into an excellent shot-heater. In this respect, too, its capabilities were 

 fully tested in the experiments previously mentioned. The application of 

 the machine to the purpose of ventilating public buildings and ships was 

 next illustrated. The application of the fan to this purpose is not new ; 

 but, as usually constructed, it requires a very considerable amount of 

 power to impel it, a great proportion of which is absorbed in overcoming 

 the inertia of its mass, and sustaining it in rapid motion. In the form 

 given to the fau by Mr. Chaplin, however, the resistance arising from 

 friction and ineitia is reduced to a minimum, and the power applied is 

 almost wholly employed in exhausting or pumping out the vitiated air, 



