102 ENGINEERING FOR LAND DRAINAGE. 



tracings. They are made as follows: Make a copy of 

 the map it is desired to print upon tracing-cloth or 

 upon a transparent paper, taking care to make all of the 

 lines definite and black. Place this copy with its face 

 side against the glass of the print frame. This frame 

 may be made of a strong picture-frame of sufficient 

 size to take in the drawing. The back should be made 

 firm and so arranged that it can be clamped closely to 

 the glass by means of buttons attached to the back of 

 the frame. Upon the drawing or map place a piece of 

 the prepared paper, the prepared face against the trac- 

 ing, and place some smooth papers or layers of cloth 

 upon the back of it and clamp the backing board firmly 

 against it, so that every part of the tracing will be 

 firmly pressed against the glass. The prepared paper 

 can be bought of dealers in engineers' supplies. It 

 should be kept in a dry and perfectly dark place. 

 When both tracing and paper have been arranged in 

 the frame as above directed, expose the glass to the 

 direct rays of the sun for four or five minutes if the sun 

 is bright. Take out the paper and place it in a bath of 

 clear water. Move the water over it until the paper 

 turns a clear blue and the lines show a clear white. 

 Then hang up to dry. If the blue is too light, the ex- 

 posure was too short ; if too dark, it was out too long. 

 If paper which is not fully transparent is used as a 

 copy it must be exposed longer than a perfectly trans-- 

 parent negative. A little practice will soon enable the 

 novice to make good prints. 



