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<p>[QUOTE="calcol, post: 3098308, member: 77639"]When I actively collected ancients, I measured SG on some, mostly as a learning and fun experience. There have already been excellent comments on equipment and procedure in this thread. There are a couple more things: 1. Draft shield for your apparatus. This can be fancy, like sheets of acrylic plastic, solvent-welded to make a box with an opening. Basically a plastic aquarium on its side. Or simple, like a wire or wood frame covered with thin plastic sheeting.</p><p><br /></p><p>2. This is optional: The accuracy of SG measurements is improved by using immersion liquids with a density greater than water. I won't go into the detailed math/statistics on it. Briefly, measurement of SG by immersion weighing is relying on the difference in weight in air and when immersed. The error of the two weights is about the same, so if the difference between them can be made greater, then the percentage error of the calculated answer (i.e. SG) will be less. The weight difference will increase with increasing density of the liquid.</p><p><br /></p><p>The liquid of choice for small metal or mineral objects is perfluoromethyldecalin. It has a density twice that of water, is inert, has low surface tension (few bubbles adhering to the object), and evaporates quickly. Think of it as liquid teflon that evaporates. It's expensive, but will last a long time. Only a small amount is lost with each measurement.</p><p><br /></p><p>Cal[/QUOTE]</p><p><br /></p>
[QUOTE="calcol, post: 3098308, member: 77639"]When I actively collected ancients, I measured SG on some, mostly as a learning and fun experience. There have already been excellent comments on equipment and procedure in this thread. There are a couple more things: 1. Draft shield for your apparatus. This can be fancy, like sheets of acrylic plastic, solvent-welded to make a box with an opening. Basically a plastic aquarium on its side. Or simple, like a wire or wood frame covered with thin plastic sheeting. 2. This is optional: The accuracy of SG measurements is improved by using immersion liquids with a density greater than water. I won't go into the detailed math/statistics on it. Briefly, measurement of SG by immersion weighing is relying on the difference in weight in air and when immersed. The error of the two weights is about the same, so if the difference between them can be made greater, then the percentage error of the calculated answer (i.e. SG) will be less. The weight difference will increase with increasing density of the liquid. The liquid of choice for small metal or mineral objects is perfluoromethyldecalin. It has a density twice that of water, is inert, has low surface tension (few bubbles adhering to the object), and evaporates quickly. Think of it as liquid teflon that evaporates. It's expensive, but will last a long time. Only a small amount is lost with each measurement. Cal[/QUOTE]
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