 Welcome to the series, Photographic Chemistry, presented by the Foundation of the American Institute for Conservation of Historic and Artistic Works. This program was made possible by grants from the National Endowment for the Humanities and the Andrew W. Mellon Foundation. Each program in this series is presented as a short video. Depending on your video viewer, you should be able to pause, return to a previous section, or skip ahead to a later section by using a scroll bar or on-screen icons. You will find an outline of the course and short quizzes to test your understanding on the course webpage. The KSP value communicates the magnitude of the solubility of a material within a solvent, in our case, salts and water. We use these values to be able to understand the properties of these photographic materials in our photographic process. And I'll refer to these KSP values quite often as we talk about photographic chemistry. To illustrate in the table shown, I'm comparing the relevant silver halide grains of silver chloride bromine iodine with something we know a lot about, table salt. And as you can see in these KSP values at room temperature, there are orders of magnitudes. When a scientist has orders of magnitudes, these are factors of ten difference between table salt and sodium chloride. In fact, if you just compare the ratios, compare the numbers, sodium chloride is about 700 million times more soluble than silver chloride. 700 million times. Or we would say that that's about eight orders of magnitude difference between the solubility of sodium chloride and silver chloride. And if you compare the values, you can now understand that there are even big differences between the silver halides, the silver chloride bromides and iodines. And this is a key point. These are the values we use to engineer and develop specific silver halide grains for specific applications. The composition of a grain is very much determined by these KSP values when we go to do an emulsification process. Now you'll see KSP values in two different forms, either in the KSP or if we want to communicate rather than always saying 1.77 times 10 to the minus 10 all the time, we do the same trick that we do for pH. The little p means negative log of. So I can take these bigger numbers and convert them into the negative log of values, much like we do with pH. So 1.77 times 10 to the minus 10 is equal to 9.75 pKSP. You just have to be a little bit more comfortable with that number because what this means is, remember in pH, the higher the pH, the less H there is in solution. In other words, a pH of 14 means a sparingly small amount of H plus in solution. It's mostly basic or OH, and we'll get to that. Same is true here with the pKSP. The higher the value, the less of it that there is, the smaller the magnitude of the number. So we see that between sodium chloride and silver chloride, there's an 8 order of magnitude difference. Each click of the number is a factor of 10. So there's 8 factors of 10 difference, or that's 700 million, roughly, right? That's 700 million time difference in the solubility between silver chloride and sodium chloride. And there's even an additional 7 orders of magnitude difference between silver chloride and silver iodine. This is the key point. So get used to understanding these numbers. These are very, very small numbers, and what that means is that these are very, very insoluble salts. What this means is that the concentration of ions, and this goes back to the definition of KSP, this means the concentrations of ions in solution can be no more than these very, very small values in molarity. So let's see how we use these KSP values in the emulsification process. You have completed this unit. Depending on your video viewer, you should be able to scroll back to any point in the video as desired. The short quiz found in the course materials on the website may help you confirm your understanding of the concepts introduced here. Many thanks to the instructor, production editor, coordinator, and the collaborative workshops and photograph conservation committee for their work to make this program possible.