After reviewing links on my 2009 blowpipe tests post (spurred on by this recent comment on another post), I decided to do a little more research concerning field tests for gold, silver, and other metals (primarily; some of these links are for minerals in general, though I haven't included links for the usual hardness, scratch, and other well-known tests and characteristics). The articles and books listed below may include information about blow-pipe tests (B) or info about other types of tests (O). Some include general gold, silver, and other metal or mineral prospecting information (P), many include information about other metals or elements besides gold and silver (ME), a few include info about minerals, not just elements (M), and a couple are more unknown in their coverage because they are not available in full online (U). I've listed them by year.
Merritt, W.H., 1911, Field Testing for Gold and Silver: A Practical Manual for Prospectors and Miners: Crosby Lockwood and Son, London. (B, O, P)
Osborn, H.S. and Von Bernewitz, M.W., 1920, Prospector's Field Book and Guide: Henry Cary Baird & Co., Inc., New York. (B, O, P, ME, M)
Davison, E. H., 1937. Field tests for minerals [snippet view only]. London: Chapman & Hall. (M, U)
Fansett, G.R., 1940, Field Tests for the Common Metals: Arizona Bureau of Mines Bull. 147. (B, O, P, ME)
Stevens, R. E., and Carton, M. K., 1948, Simple field test for distinguishing minerals by abrasion pH: American Mineralogist, v.33, p. 31-50. (O, M)
Roseveare, G.H., 1966, Field Tests for the Common Mineral Elements: Arizona Bureau of Mines Bull 175. [this appears to be a reprint or update of ABM Bulletin 147 linked above] (B, O, P, ME)
Franke, W.A., (no date, prob 1990s), Quick assays in mineral identification, A guide to experiments for mineral collectors and geoscientists in field work. Published online. (B, O, ME)
Pray, R.E., 2006, How to Prospect for Silver Field Tests You Can Use to Detect the Hidden Metal [abs only, or subscription required]: ICMJ's Prospecting and Mining Journal (P, U)
Basic Field Tests for Gold and Various other Metals - at Nevada Outback Gems (O, P, ME)
And of course there now is portable or handheld xrf. This is my favorite model (although I've used only two models from one manufacturer).