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BELL SYSTEM TECHNICAL JOURNAL 



of all kinds of street pavements preparatory to laying underground 

 conduit, cutting frozen ground, loosening the earth in excavating 

 instead of using picks, drilling rock preparatory to blasting for under- 

 ground conduit or for pole holes, tamping back filled earth, cutting 

 iron pipe covering from cable, etc. 



Fig. 20 — Air Compressor Mounted on Trailer for Maximum Portability 



Fig. 20 shows a new type of portable gasoline engine driven com- 

 pressor unit which is being satisfactorily used for the larger jobs of 

 opening street pavements, for rock drilling, etc. 



Fig. 21 — Removing Granite Blocks and Breaking Concrete Base 



