3« 



THE ALUMNI JOURNAL. 



Now, to-day we do the same work 

 with that apparatus (exhibiting appar- 

 ently a Kodak), and a great deal better 

 work it is. 



1111871a more important revolution 

 took place even than the wet plate pro" 

 cess or the daguerreotype, Many efforts 

 had been made to overcome the use of the 

 wet plate — the plate wet with nitrate of 

 silver, and some of the efforts were very 

 successful but usually troublesome. The 

 plate was kept moist in a variety of ways: 

 by honey, by tea, by infusion of tea, by 

 beer, by coffee, and a multitude of all the 

 funniest concoctions you could think of, 

 but the process was destined to fail. 



In about 1870 it was conceived that 

 3'ou could make an emulsion of these 

 peculiar compounds of silver — these sen- 

 sitive silver compounds — that you could 

 make an emulsion that you could pour 

 upon the plate and produce a picture just 

 when you pleased, and it was found that 

 by mixing the chloride that produces the 

 sensitive material in one portion of your 

 collodion and putting nitrate of silver 

 into another portion of the collodion, in 

 certain proportions, you could produce a 

 collodial emulsion. They had to be 

 mixed in just exactly the right propor- 

 tions, so as not to have an excess of ni- 

 trate of silver or an excess of bromide. 



But that process failed and only lasted 

 a few years; although I have here one of 

 the plate holders used by such a process. 



This was between the time of the wet 

 plate process and the modern dry plate, 

 when they used collodial bromide emul- 

 sion. It was a kind of a compromise be- 

 tween the wet plate and the dry plate. 

 In 187 1, Dr. R. L. Maddox, of Bath, Eng- 

 land, had the idea that he would use 

 gelatine, instead of albumen or collodion, 

 as a vehicle to hold these silver salts 

 upon the glass surface, and he found, 

 among other things, something that sur- 

 prised him — that when he put the silver 



it:-; i.i to contact with this gelatine they 

 became wonderfully more sensitive than 

 ever before. 



The idea is this : That you make a 

 gelatine mixture of a certain strength — 

 the proportions required a certain amount 

 of soft gelatine and a certain amount of 

 hard gelatine. Into that gelatine you 

 pour, with constant stirring ; you pour 

 a mixture at the same time — some par- 

 ticular bromide, generally bromide of 

 potassium and nitrate of silver — in a 

 very thin stream and keep it thoroughly 

 stirred up. If you go too fast, you will 

 not get the right result ; but the result 

 is, when you get through and doit right, 

 you get a beautiful milky fluid, and that 

 fluid contains bromide of silver in a won- 

 derful state of suspension — very thin — 

 and it remains suspended in this fluid. 

 Now let that set — this cream or " emul- 

 sion," as they call it — and you have as a 

 result iodide of silver and iodide of potas- 

 sium. You let the emulsion set and it pro- 

 duces a jelly, that jelly is then cut up into 

 shreds, rubbed through a sieve or some- 

 thing of that kind to make it thoroughly 

 divided, and washed thoroughly with 

 water. Having done that it can be 

 melted, and if you melt it and heat it to 

 a certain temperature, there does not 

 seem to be any limit to the sensitiveness 

 of the material. If you use it cold it 

 requires a second or two to produce a 

 picture. If you cook it, however, you 

 will find that it will become more and 

 more sensitive to light, until it is actual- 

 ly possible to take a picture of a pro- 

 jectile traveling four hundred metres per 

 second. I have such a picture. The 

 only trouble is that some of the plates 

 made are so sensitive to light that we 

 cannot get a light non-active enough to 

 develop them. Having these bromide 

 plates then in the camera — this sensitive 

 material coated on these glass plates in 

 the camera — you have got to be very 



