Читать книгу A Practical Manual of the Collodion Process. Giving in Detail a Method For Producing Positive and Negative Pictures on Glass and Paper онлайн

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Nitrate of Potash (saltpetre) should be dry and finely-powdered. I use none other than Dupont's refined; this is very nearly, if not absolutely, chemically pure.

The commercial Sulphuric Acid (oil of vitriol) of America is of great uniformity of strength, as sold by druggists generally. I use a test-bulb graduated to the proper density, and have been very successful in my experiments.

In some twenty different samples of acid, used in different cities in the United States, I found only one that produced a poor cotton, and this might have been influenced by the moisture of the atmosphere, it being a very rainy day when I used it.

During my recent and somewhat extensive practice, I have thought that the fine long fibres of cotton wool do not make so desirable a soluble cotton as that which is heavy or common. Four or five very careful experiments upon this point, have had the effect to produce in me a strong belief that my ideas are entitled to some consideration. I should not select the finest cotton for making soluble cotton, but now invariably take that which is thick or coarse.