300 



Popular Science Monthly 



and developer from soaking through to 

 the drawer below. The use of a water- 

 bath for keeping the developer cool will 

 be found a great convenience. It will 

 be noticed that the running water in the 

 wash-tank is in contact with the hypo- 

 tank, thus insuring cold hypo. In case 

 it is intended to work with only small 

 plates or films the hypo and wash tank 

 shown in Fig. i to 4 may be supplanted 

 by the one shown in Fig. 5. This 

 consists of a galvanized-iron tank i ft. 

 square and i ft. high, which serves as a 

 wash-tank. In this, at one end, is 

 placed a glass or hard rubber battery jar 

 such as may be obtained from any of the 

 larger electrical dealers. This jar serves 

 as a hypo-tank. 



The rheostat. Fig. 2, is a 300-ohm 

 rheostat of half-ampere capacity and has 

 all the range needed for dimming a 50- 

 watt red lamp. If a "dimalight" is 

 obtainable it will be found to be a 

 satisfactory substitute for the rheostat. 

 Care should be taken to paste a piece of 

 black paper over the tip of the red lamp 

 as the tips of such lamps are often 

 uncolored, allowing white light to pene- 

 trate into the room. 



In Fig. 2 the white light is shown as a 

 lOO-watt Mazda C-2 lamp behind a 

 ground glass. It therefore serves both 

 as a white light and as a diffuse light for 

 printing. 



Attention is called to the use of cur- 

 tains in the doorway as a means- of 

 economizing space in case the dark- 

 room is built out like a closet in a large 

 room. Two curtains are hung on sep- 

 arate rods as shown in Fig. 6. The out- 

 side edges are fastened permanently to 

 the doorway. The inside edges are 

 fastened to sticks about i in. square. 

 These sticks act as weights and prevent 

 the curtains from blowing in and out, 

 causing light-leaks. Each curtain is 

 wide enough to stretch completely across 

 the doorway. A suitable housing as 

 shown, painted black on the inside, 

 prevents light from leaking over the top 

 of the curtains. The curtains are made 

 of double thicknesses of galatea. Such 

 a closet darkroom requires artificial 

 ventilation or it soon becomes unbear- 

 able. An adequate scheme for ventila- 

 tion is suggested in Fig. 2 and 7. 



The second darkroom is more elabo- 

 rate and is more adapted to professional 

 use. The tanks and their arrangement 



are shown in Fig. 8, 9 and 10. The cost 

 of construction may be reduced by sub- 

 stituting the hypo and wash tank shown 

 in Fig. 5. Attention is called to the 

 method of drying the plates with the 

 fan. The hypo and wash tank is shown 

 in detail so as to be a guide to any who 

 may care to construct a similar one. In 

 Fig. II the switches governing the 

 various lamps are not shown. The 

 treadles will, however, indicate where 

 these switches should be placed. In 

 Fig. 12 is shown the general arrangement 

 of tanks in a closet darkroom. 



A Comfortable Collar for 

 the Horse 



PADS used in the construction of any 

 article add proportionately to its 

 weight and in the making of horse collars 

 the added burden is considerable; yet 

 it is quite necessary to have sufficient 



Air cell substitute is more comfortable 

 than the stuffed pads in a horse collar 



padding against the horse's shoulder as a 

 protection. The latest type of a collar 

 made abroad is a pneumatic pad, built 

 up similar to an automobile tire. Each 

 side of the collar is a chamber of suitable 

 shape to receive an inner air tube, which 

 is blown up with a tire pump. Not 

 only is the collar lighter than the 

 ordinary one but it will fit better on the 

 neck of the horse. 



