144 



SHADE-TREES IN TOWNS AND CITIES 



the leak and aerating the soil. This can be done by leaving 

 the ditch open, digging a channel around the tree, loosening 

 the soil about the roots, and watering freely. 



Laying of Gas-Mains. Care in laying gas-mains is of the 

 utmost importance. The leaking of gas is a great loss to 

 the gas companies, and economizing the cost of first con- 



D A F B C E 



yp ^ 1 | r*' 'i h 



Fig. 27. Method of making- tight joints in gas-pipes. A, Untarred oakum or 

 hemp. B, Calked lead. C, Rubber packing. D and E, Two malleable 

 iron sectional rings. F, Bolts for drawing the rings together so as to press 

 down rubber packing C. G, G, Wooden blocks for supporting ends of pipes. 



struction is likely to prove disastrous in the long run. 

 Sometimes gas-pipes are laid with cement joints, as this 

 method is cheap ; but the least settling of the ground causes 

 leaks. Threaded joints are efficient on small pipes. One of 

 the best methods now in use of making tight joints in gas- 

 pipes, eight inches or more in diameter, is shown in Fig. 27. 

 Untarred oakum or hemp-yarn is well rammed in first ; and 

 above that is poured melted lead, which is afterward com- 



