THE WORLD'S ADVANCE 



219 



Acid Cuts Hole in Glass 



Hydrofluoric acid will cut a hole 

 through glass in short order. A dam of 

 wax should be placed about the spot 

 where the hole is to be made, and into it 

 a few drops of the acid should be poured. 

 Hydrofluoric acid will dissolve nearly all 

 substances, and it should be handled 

 carefully. It is sold in small wax bot- 

 tles. 



Contributed by 



THEODORE GOTHMANN. 



A Makeshift Marking Gauge 



A marking gauge that will answer for 

 most purposes about the experimenter's 

 workshop can be constructed along the 

 following lines : 



A long, true rod of brass or iron should 



be bored at one end with two holes, one 

 for a marking point and the other for a 

 set screw to hold the marking point, or 

 scribe, in place. Referring to the draw- 

 ing, B is a block of hard wood bored with 

 a hole which should be threaded to ac- 

 commodate a wing clamp screw. A is 

 a larger wood board of thinner material 

 along which the object to be marked 

 slides. 



Contributed by 



JAMES J. ROGERS. 



Knife Switch Controlled by Cords 



A knife switch located on the ceiling 

 can be controlled by two cords, if two 

 stiff metal strips are brought out to a 

 point, one from the hinged end of the 

 blade and the other from its centre and 

 riveted as shown. One cord should be 

 fastened to the end of the two strips 

 and the other knotted through a hole 



bored in the handle. Pulling on cord G 

 closes the circuit; pulling on cord C 

 opens it. The metal strips are indicated 

 as BB in the drawing. 

 Contributed by 



EARL B. WILLIAMS. 



Freeing Sash Weights 



Sash weights which have become 

 jammed can usually be freed by remov- 

 ing the pulley and prodding. A length 

 of stiff wire or an ordinary kitchen poker 

 will do. 



Contributed by 



WM. C. HOUGHTON. 



To Reinforce a Strained Brake Shaft 



An automobile brake shaft which has 

 become bent through repeated strains and 

 jolts can be stoutly braced with little 

 trouble, so that further bending is 

 avoided and the possibility of the shaft 

 breaking is eliminated. A strip of heavy 

 steel should be bent at the middle to fit 

 snug about the shaft and its two ends 

 brought back and riveted to the cross 

 beam. 



Contributed by ADOLPH KLEIN. 



