M. TECHNOLOGY. 521 



unite the joints of his apparatus in such a way as not to 

 allow the leakage of air under an ordinary pressure often to 

 fifteen pounds to the square inch. Whenever possible, glass 

 tubes should be united at the joints by fusion, and when this 

 is impossible mercury joints should be used, and it is found 

 that the best way to construct these is to have a well-made 

 perforated conical stopper of very pure India rubber let 

 into the wide funnel tube of the joint and carrying the nar- 

 row tube. Before fitting the tubes into the India rubber, 

 this is heated in a spirit-lamp until its surface is decomposed. 

 It is then fitted into its place, mercury poured over, and oil 

 of vitriol on the top of that, and when well made this joint 

 seems entirely secure. Ordinary India-rubber joints are of 

 no use in these experiments, as Avhen the vacuum is nearly 

 perfect they allow oxygenized air to pass through as readily 

 as the pump will remove it. A cement that lasts satisfac- 

 torily for a few hours, but not over a day or two, is made 

 by a mixture of eight parts of resin and three of beeswax. 

 7 A, XL VIII, 86. 



TO PREVENT SHAFTING ACCIDENTS. 



Many suggestions have from time to time appeared upon 

 the subject of preventing or lessening the liability to acci- 

 dents arising from the entanglement of some portion of an 

 operative's garments in a swiftly revolving shaft, which 

 accidents are of too frequent occurrence in our large manu- 

 factories, and are of a distressing or fatal character. One 

 of the simplest methods of rendering these casualties impos- 

 sible, without introducing the necessity of constructing a 

 railing or fender about the moving piece in dangerous places, 

 is to cover the shaft with a loose sleeve alono" its entire 

 length. This may be made of sheet-tin or zinc, and to be 

 removable if desired. It should be covered within and at 

 the ends with leather, to prevent noise. Arranged in this 

 manner, the friction between it and the revolving shaft 

 would be sufficient to cause the sleeve to rotate with the 

 latter; but in the event of any decided resistance being 

 brought to bear upon it, as in the case of the engagement of 

 a workman's garment, the sleeve would at once be brought 

 to rest, and permit of its extrication without accident. The 

 same idea of loose covers may be applied to cog-wheels or 



