MIXING.
A suitable vessel must be obtained for mixing. It is. perhaps, more that this should be opaque, or of a rub, or orange colour. Further, it must have I a wide mouth, to allow of stirring, and easy addition of other solutions. It must be glazed and free from cracks, preferably pos sessing a lid which can be made to fit down I quite light-tight. Ointment pots, capable of holding to or 12 oz., certainly seem very suitable. There is a form, similar to that ' shown in the illustration, which has been I found very convenient. Having chosen a suitable vessel, it must be stood in a saucepan or anything capable of holding hot water (see Fig. 131). For experimental purposes, an ordinary enamelled mug, now obtainable at most hardware shops, may be used. The advantage over a saucepan if that there is no handle liable to be knocked against in the dark. When the gelatine is completely dissolved, winch may be aided by stirring it all the time with a glass rod, pour in the silver nitrate, and beat up thoroughly together, to ensure its being completely mixed. All the operations up to this point may be con ducted in ordinary white light ; but the following, in which the emulsion is be pulled in two, which brings it to a fine point, as shown in Fig. 133. When cold
the extreme end is snipped off, and leaves a tiny hole through which the solution can pass. The tube, B, remains above the solution, and by blowing through it the solution is forced up through the tube, A, and emitted in a fine spray. Fill the sprayer with the solution of potassium bromide, and insert the cork and tubes, so that the tube, A, is almost, but not quite. on the bottom ; this will ensure all the solution being driven out. Hold the sprayer in the left hand, apply the lips to the tube, B, and blow through same, all the time stirring the gelatine solution vigorously with a glass rod. For stirring the emulsion, a glass spatula, or a flat strip of glass tied with white thread to a glass rod, will be found exceedingly useful. Do not get the spray too near, or ,..Jrnmed, must be carried out in a red light, of which the less the emulsion is exposed to the better.