124 PHOTO-MICROGEAPHY 



be left in the hypo some little time — say five minutes — after the last trace of yellow- 

 ness has vanished. 



Let us now examine our negative in front of a gas flame with a piece of ground 

 glass interposed between the two — the flame and the negative. If the exposure 

 and development have been correct the proboscis should be very clearly shown 

 upon a black background, and if the focussing has been perfectly carried out, 

 the little hairs protruding froni the lobes of the organ should be quite plainly 

 seen sharply defined ; so, too, ought the edges of the suctorial tubes, as well as 

 the small hairs when looked at through the focussing glass, applied, of course, 

 to the back of the negative. It should be noted that as the proboscis itself is not 

 absolutely flat it is impossible for the whole of the object to be absolutely in one and 

 the same focus. Should, however, the negative appear choked, and the clear portions 

 of glass between the rings of the suctorial tubes overcast with shadow — blotted out, 

 in fact— and the background so pitch dark that the gas flame can scarcely be seen 

 through it, we know that one of two things has taken place — either we have over- 

 exposed our plate or else we have over-developed it — perhaps both. One other 

 alternative may possibly be seen, a faint or perhaps a fairly defined image of the 

 proboscis, visible upon a background far too transparent. This is a common fault 

 and it occurs most frequently to those commencing. It produces a positive with a 

 muddy background, superimposed upon which lies the image of the proboscis faintly 

 and sickly defined. This arises from under-exposure, and nothing we know of will 

 cure it save taking another picture. 



Supposing we wish to save a picture which is overcast and evidently over-exposed 

 or developed, we may do so in a great measure by allowing it to dry after washing 

 a couple of hours in water, to rid it of its hypo, and then again placing it in water 

 for a few minutes while we are preparing the thinning solution. Of these there are 

 many, and each photographer may be said to have his pet formula ; the one we 

 prefer at this stage is that adopted by most photographers in the trade. It is simple 

 enough to make, and eflicacious to use, but, seeing it is desperately poisonous, must 

 be handled vdth extreme care, and the operator must be provided with an india-rubber 

 finger-stall for any finger with a hang-nail or open scratch. To make the solution 

 one proceeds as follows : Place one or two pieces, about the size of a very small 

 marble, of cyanide of potassium in about i oz. of water in a measure, and when 

 dissolved or nearly so, add 20 or 30 drops of a very concentrated solution of iodine 

 in spirits of wine. The brown solution of the iodine instantly disappears as it is 

 added to the cyanide. The iodine solution must be very strong, at least three or four 

 times that of the liq. iodi of the British pharmacopoeia. Having stirred well with a 



