Tin pipes, and copper pipes, lined with tin, have been proposed as substitutes for lead pipes, but they are too expensive.

The lead encased pipe, made under Haines's patent, has, however, been found to be perfectly successful.

This consists of an inner pipe of block tin, encased in a lead pipe as shown in section, Fig. 146. The two metals are so united that no joint between them is perceivable, and they cannot be separated by any amount of bending or twisting.

In consequence of the tin melting at a lower temperature than the lead it is somewhat difficult to make a soldered joint in these pipes. However, it may be done with care, or Heap's mechanical joints may be used, in which the union is effected by means of screwed couplings.

Fig. 146.

## Weight Of Lead-Encased Pipe

As the lead-encased pipe is stronger than ordinary-lead pipe, it may be of less weight per yard for water supply under any given pressure. To meet the case in which water companies require pipes to be of a certain regulated weight according to the head, a special lead-encased pipe is made with a smaller proportion of tin. The weights of pipes of this class are shown in cols. 9, 10, 11 of the Table below. They are heavier and cheaper than the pipes with full proportion of tin, whose weights are given in cols. 6, 7, 8.

## Table Of Weights Of Lead-Encased Pipes In Lbs. Per Yard Run

 Internal diameter in inches. Extra light Weights. Weights suitable for supply of water under the heads stated. Extra heavy weights with less tin for supply of water under heads stated. 50 feet head and under. 51 to250 feet head. 251 to500 feet head. 50 feet head and under. 51 to250 feet head. 251 to500 feet head. 3/8 1 1 1/2 2 .. 2 1/2 3 3 1/2 4 4 1/2 5 1/2 2 2 1/2 3 .. 3 1/2 4 44 5 6 7 5/8 3 3 1/2 4 .. 4 1/2 5 1/4 6 7 8 9 3/4 . 3 1/2 4 41/2 5 51/2 6 7 8 9 10 1 4 1/2 5 51/2 6 71/4 8 9 10 11 12 1 1/4 6 1/2 7 8 .. 9 10 12 124 14 16 1 1/2 8 9 10 .. 11 12 1/2 14 16 18 21 2 11 13 .. .. 16 18 1/2 21 23 26 30 No. of column. 2 3 4 5 6 7 8 9 10 11