VOL. 6. No. 4
A SAW~CUARD *OR STOCKSOLUTIONS
735
Only the lower portions of the supply lme and safety tube are shown in the sketch. For the 50% NaOH and similar viscous solutions care should be taken not to use less than tubing, or the rate of flow will be slow.
A SAFEGUARD FOR STOCK SOLUTIONS E. F.ALMY, OHIO STATE UNIVERSITY, COLUMBUS, OHIO In using standard solutions drawn by siphoning from stock bottles into burets equipped with two-way stopcocks loss of solution has occurred several times due to rupture of rubber tubing used to connect the lower end of the supply line to the buret. If this happens when no one is in the laboratory the entire stock of solution is lost. The device sketched in the accompanying figure has solved the problem, and no further losses have been experienced since it was installed. A piece of 1" x 3" strip A serves as the frame-work for the device. A if' hole B is bored in this and a pinch-cock C is mounted in front of the hole. The pinch-cock is supported somewhat away from the frame by mounting it on the 3'' block D, and is held in place on this block by staples as a t E, and by the block of wood F. The pinch-cock is operated by the lever G,held to the frame by a screw H and with washers I on each side of the lever. The lever may be operated from below by pulling or releasing the string J , which extends down to the level of the buret. In use this frame A is mounted a t a level just above the highest solution level desired in the stock bottle, by fastening it to the shelf with upright strips a t each end. A section of rubber tubing K is put in the supply line passing from the glass siphon coming from the stock bottle through hole B from the back of the frame to the front and is there connected to glass tubing leading down to the two-way stopcock of the buret. To operate the device after the siphon is started, simply turn the twoway stopcock to allow liquid to enter, and pull gently on the cord. By controlling the tension used the liquid flow can be held a t any rate desired. If preferred, the pinch-cock can be held open by pulling the cord down, and the two-way stopcock used to control the rate of filling. In case of a break below the guard only the liquid below it is lost. If the break is above the guard the liquid in the siphon simply flows back into the bottle.
