Sept., 19o7.] Notes and Comments. 223

c i r c u m s t a n c e s . T h e wel l is 343 f e e t deep , w i t h an e i g h t - i n c h

c a s i n g a t t h e top .

F i g . 7 s h o w s an o ld w a s t e d u m p , c o n t a i n i n g s o m e t h i n g l ike

5000 cub i c y a r d s of m i x e d g o b , o r e a n d di r t . S o m e of the

m o s t p e r f e c t e x a m p l e s of m a l a c h i t e w e r e f o u n d in t h e p r o c e s s

of e x c a v a t i n g p a r t s of th i s d u m p . T h e g a r d e n s h o w n in t h e

i m m e d i a t e f o r e g r o u n d is t h e s i te of t h e d e p o s i t i o n b u i l d i n g

s h o w n in F i g : 6. T h i s p h o t o g r a p h was m a d e d u r i n g t h e p e r i o d

of c o n s t r u c t i o n in I9OO-I9OI , as w e r e t h o s e r e p r o d u c e d in o t h e r

p o r t i o n s of th is a r t i c l e .

E L E C T R O L Y T I C C O R R O S I O N OF IRON AND STEEL IN CONCRETE.

In a paper read at the two hundred and fourteenth meeting of the American institute of Electrical Engineers at New York, March I, 19o7, A. A. Knudson presented the results of research he had carried on for sev- eral years to ascertain whether concrete will afford iron and steel the same protection from stray currents of electricity as it gives against ordinary corrDsion or rust. In addition to the laboratory experiments detailed the author of the paper refers to two practical cases of the recognition of electrolytic action in important steel structures. The first of these is the bridge over .the Gowanus Canal, South Brooklyn, N. Y., at Hamilton avenue. The Bridge Commissioner, in his report for the year ending June 30, 19o6, said that the foundation walls developed some rather serious cracks on both sides of the canal, with a movement of the walls toward the center of the canal.

E L E C T R O L Y T I C A C T I O N O N B R I D G E S T E E L .

To ascertain the electrical conditions, Mr. Knudson made some tests at the above mentioned bridge, the results of which are thus stated:

The voltmeter readings show the steel structure to be positive to the canal, positive to water mains in the street, and positive to the trolley rails on the bridge, ranging from o.5 to 1.5 volts. These readings were taken when the car traffic was light. Some of the cracks on the concrete had been plastered over, but others were quite visible. The tests indicate that the trolley tracks on the bridge are in connection with the steel structure. Tests were also made on another bridge of tt/e same construction a little further north over the same canal, at Ninth street. The readings here were exactly the reverse to those found at the Hamilon avenue bridge, the structure being negative to canal, water mains and tracks. There were no visible cracks in the concrete of either foundation. Although the cracks in the concrete of the Hamilton avenue bridge are attributed to other causes in the commissioner's report, we believe these tests and observations point strongly to electrolytic action fro~m trolley currents as being the