 We'll talk about using organic elemental analysis for the identification of cellulose nitrates and I will focus on the X-ray films. So I will start with a bit of history about the development of the X-ray film and then I will try to explain how we got to the organic elemental analysis. So as we know the X-rays were discovered by Redgen in 1895 and by then there were plenty of materials available to use the supports for the development of the radiographic image. And so we know that in 1878 we have the first production of cellulite and in 1878 we have the use of cellulose nitrate as a substrate medium for the photographic negatives. However, for the development of the radiographic image the preferred medium was glass plates and they were used I think from 1896 there was a successful design which prevailed and they were using glass plates for their radiographic purposes. And it carried on until there was World War I and what happened then where there were two main reasons why there was a need for an alternative support. First of all there was a need of portable X-ray apparatus for the field hospitals so glass plates were not the ideal support. And the second one was that the main source of the glass was from Belgium and Belgium obviously wasn't accessible because of the war. Therefore in 1914 we have the introduction of the single coated cellulose nitrate X-ray film but that was a bit problematic because it curled extensively so the development of the radiographic image in the trace was a problem so that led to the double screen technique by 1916 and the addition of the non-curling film base which eventually finally it brought the double-sided film on cellulose nitrate base by 1918. And eventually just a picture of how the double coating works on the radiographic film and of course there wasn't just a single one-fire there were many fires that occurred because of the flammable nature of the cellulose nitrate and by 1924 we have the introduction of cellulose acetate for the X-ray film and but in 1929 there was a massive fire at the Cleveland Hospital which was triggered by the X-ray film collection and I think that prompted the discontinuation of the cellulose nitrate for radiographic purposes in the United States by the year 1933. I stress that in the United States because in the UK carried on the Ilford Limited produced both X-ray films on cellulose acetate and cellulose nitrate from 1932 and for many years so eventually we reached the 1950s when we can say that we have the discontinuation of cellulose nitrate worldwide. So now in the Natural History Museum we have a small collection of film and negatives of photographs and photographs but we have a much larger collection of X-ray films and the X-ray film collection exists because actually we also have an X-ray lab which was set up in the mid 1930s and it has been in use ever since by the curators and researchers which would like to study the skeletons of specimens by developing X-ray films by studying them for the X-ray film. So that means that it was expected that in our collection we will have cellulose nitrate X-ray films. So the identification though was a bit tricky because what happened was when it came to the photographic film and the role film is very straightforward. You have the edge printing, you have notches so you can identify the film based on that. However with the X-ray films unfortunately I didn't find any edge printing classifying it as nitrate or any notches at least in the collections that I surveyed. The only thing I found was the only edge printing that I did find was that of safety and that wasn't very helpful obviously when you want to try to identify cellulose nitrate instead. So I had to think of the alternative ways of the identification and one is the degradation to check the degradation pattern which can be very helpful when you do have degradation but as it happens with the X-ray film on cellulose nitrate I couldn't find a single one that it was degraded so that was a bit of a problem. So then I had to go for a destructive test. I have highlighted here just the flow test because that was the one that I used. I didn't go for the Diffen-Nilamine spot test because well the solution is corrosive, quite corrosive but that doesn't mean that the flow test is better because you use trichlorethylene which is carcinogenic but at least it was a bit more straightforward with the flow test because you just need a test tube and the trichlorethylene and then you just check whether it floats or it sinks. So if the sample float its cellulose acetate, if it sinks then its cellulose nitrate. However the flow test and the literature does say that it's not 100% reliable and if you remember because of the structure of the X-ray film it proved that it is even more so unreliable when you try to identify cellulose nitrate. So I had to continue with a different way of identification and I took six samples to be analyzed on the FTIR and we used the attenuated total reflectance FTIR of the VNA which is next door to Natural History Museum. It's very useful to have such neighbors. So we had six samples, we analyzed the two sides so we end up with flat spectra but only one result and that was of the coating which was we found the closest spectra was out of a cow gelatin and that was not very helpful. Obviously there is a very interesting article by Barbara Walsh on the use of FTIR analysis for the education of cellulose nitrate which it works for the photographic film but with the X-ray film being coated on both sides is tricky. Obviously you could remove the coating and then re-analyze but doing that on a sample that is no bigger than a five square millimeter is a bit laborious and tricky. So at that point we were thinking of, I was thinking of the burn test but my colleague Stanislav thought that okay if we are going to burn it maybe we should burn it in a more analytical way. So we use the organic element analysis. Now what's that? It's equipment that is the one that the analyzer that we have in the Natural History Museum is called Vario L-Cube and what it does basically is you introduce your sample into an auto-assembler roll and then that is dropped into a furnace of 1,150 degrees of Celsius and then what you see here on your left is the filter where basically it absorbs the different elements, organic elements that will come out of the fumes of the sample. So it can measure the concentration of carbon, of hydrogen, of nitrogen and even sulfur I think. But it takes some preparation before that so the sample goes into a thin boat and then you fold it very tightly so you try to extract any air, you don't want any trapped air and then and I have to add here that the sample that you use is minimal compared to the sample that you have to use to do the flow test. You can have it as little as 0.2 milligrams and then once it's wrapped as tightly in that thin boat it's dropping to you place it into the auto-assembler roll and it spurts with helium because of course we are surrounded by air and you want to exclude any atmospheric gas to interrupt with your readings and then then it burns into this furnace and the filters analyze the concentration of the elements and for the ones that we analyzed I'm just showing you here the average nitrogen concentration for the cellulose nitrate film as opposed to the cellulose acid film and we were expecting to find some nitrogen in cellulose acid film because of the coating but as you can see the percentages are the concentrations are much quite different and it actually presented the concentration of nitrogen content that we found in our cellulose nitrate films. They were compatible with what it suggested in the literature something between 10.7 to 11.8 percent. Then what we did was we want to estimate the reproducibility of our of the nitrogen content so what we did we selected three films that we knew that there was cellulose nitrate and then with Japanese screw punch we selected five samples from each of those films and from five different points and then we analyzed again and then you will see that the relative standard deviation is between 0.4 to 1.1 percent so we were quite happy with that result and it was just that we want to check that the readings that we got were accurate. So in conclusion I would say that the organic elemental analysis it's it gives you accurate and and quick results when you want to identify cellulose nitrate but I would go even further it's it's an analysis that is usually overlooked and I think since you can get to the actual concentration of the nitrogen or the carbon or the cellulose it could be it has a potential that could be used in conjunction with other analysis to study perhaps the degradation of the film and with that I would like to thank you for your attention.