“The Library of Congress announced on Wednesday the results of a survey that found that 70 percent of the feature-length films made in the United States during the silent era have been lost. The reasons range from the natural deterioration over time of highly flammable nitrate film stock to outright neglect.”

– http://carpetbagger.blogs.nytimes.com/2013/12/04/majority-of-silent-films-are-lost-study-finds/?ref=todayspaper