ABSTRACTS OF TECHNICAL ARTICLES 623 



form of the old trowelled joint, cement mortar collars molded in place, 

 and joints made with different plastic materials such as asphalt com- 

 pounds spread on a fabric backing to facilitate application and reten- 

 tion. None of these provided the tight seal desired. 



A satisfactory joint has been developed by encasing the junction in 

 a mortar bandage consisting of a wide band of cement mortar enclosed 

 in cheese-cloth and held tightly against the conduit by tapes passing 

 completely around the joint and secured on top. A separate strip of 

 cheese-cloth is imbedded in the center of the mortar to prevent slump- 

 ing. With cement mortar of proper consistency and an admixture to 

 insure the desired plasticity sufficient cement paste comes through on 

 the inside when the bandage is applied to provide a tight bond. A 

 strip of paper placed in the bandage under the cheese-cloth in the 

 outer side helps to distribute the pressure of the tying tapes and 

 assists in retaining water in the mortar thereby aiding the hardening 

 and increasing the strength of the joint. 



The results of hydrostatic tests of these joints show that they are 

 practically watertight. Their use is expected to effect savings in 

 conduit construction since their high strength permits in many cases 

 omission of the concrete base and further savings may accrue through 

 the increased speed with which conduit can be laid and joined and the 

 fact that the trench can be back-filled immediately without danger 

 of injuring the joints. Other savings in the labor of rodding ducts 

 will be realized because the new type of joint is siltproof. 



The Depth of Origin of Photoelectrons} Herbert E. Ives and H. B. 

 Briggs. Previous work has shown that the photoelectrons from a 

 silver plate covered with an equilibrium film of alkali metal follow the 

 wave-length distribution of energy just above the silver surface, i.e., 

 in the alkali metal. This question has been further investigated with 

 particular references to alkali metal films in their early stages of devel- 

 opment, where their average depth is less than one atom. Computa- 

 tions made on the absorption of light just within the silver surface 

 show that there should be very definite and striking differences in the 

 wave-length distribution of photoemission if emission occurs due to 

 light absorption in the silver, as contrasted with emission from a film 

 on the silver. Experimental tests made with sodium and caesium 

 films show that in the earliest measurable state the emission exhibits 

 characteristics peculiar to the light absorption in silver, and that as 

 the films build up the emission becomes characteristic of the energy 

 above the silver. It is concluded that the photoelectrons originate 



'^ Phys. Rev., June 1, 1932. 



