Litmus tests

We issue a mild caution. One must always be mindful of the temptation to see things not as they really are but only how they appear to be at the moment using whatever happens to be the most convenient or accepted way of looking at things. This is the dreaded solution in search of a problem phenomenon, disguised, in the case of physicists trying to make sense of the world, as the temptation to use whatever is the latest fad or theory simultaneously as a lens and litmus test for reality. 

Charych D, Cheng Q, Reichert A, Kuziemko G, Stroh M, Nagy JO, Spevak W, Stevens RC (1996) A litmus test for molecular recognition using artificial membranes. Chem Biol 3 113-120... 

Historically, pH sensitive dyes have been extensively used as indicators in acid-base titrations and in simple spot test papers, even leading to a common phrase in our everyday language, when people or topics are described as having passed the litmus test . The use of complexometric titrations for metal ions was a later but widely... 

Major depression represents a syndrome of different etiologies. Thus, various depressive subtypes may respond differently to different treatments. Unfortunately, to date, no litmus test for matching the depressive subtype to the appropriate treatment has been identified. Therefore, what we now call stage I TRD may often be more accurately construed as treatment mismatching. 

CDj) T. Urbanski, Vol 2(1965), pp 22-31 gives methods for determining the Stability of Nitric Esters, which include Abel Heat Test, Litmus Test (Vieille Test), Heat Test at 134.5°C, Silvered Vessel Test, Loss of Weight Test, Will Test, Bergmann Junk Test and Manometric Test... 

The depletion width can play a role in analyte-induced modulation of the semiconductor PL [4]. As molecules adsorb onto the surface of the semiconductor, the dead-layer thickness can change, resulting in what can be described as a luminescent litmus test When Lewis bases adsorb onto the semiconductor surface, they donate electron density to the solid, which decreases the electric field and thus decreases the dead-layer thickness. The reduction in D causes an enhancement in the PL intensity from the semiconductor. Figures 2a and 2b present typical PL enhancements observed from an etched n-CdSe substrate Relative to a nitrogen reference ambient, adsorption of the Lewis bases ammonia and trimethylamine cause a reversible increase in PL intensity. In contrast, when Lewis acids adsorb onto the surface, they can withdraw additional electron density, causing the electric field to increase and the PL intensity to decrease. Such effects have been observed with gases like sulfur dioxide [5]. 

Charych, D., Cheng, Q., Reichert, A., Kuziemko, G., Stroll, N., Nagy, J., Spevak, W., Stevens, R. (1996). A litmus test for molecular recognition using artificial membranes. Chemistry and Biology, 3, 113-120. 

Litmus test (Vieille test). This test introduced by Vieille [88] consists in warming a sample of nitrocellulose (2.5 g) or smokeless powder in a hermetically sealed test tube (Fig. 2) in presence of a band of blue litmus paper inserted within the tube. The tube is kept in a thermostat warmed to 110°C. The temperature inside the test tube is 108.5°G In U.StS.R. the temperature of the thermostat is 106.5°C. The blue paper should not turn definitely red in less than 7 hr. 

Litmus test is used to determine the acidic or basic nature of a substance or a water solution. If blue litmus turns red when dipped in a liquid, the liquid is an acid. There will be no change of colour if the liquid is a base (or water). If red litmus turns blue when dipped in a liquid, then the liquid is a base. There will be no change of colour if the liquid is an acid (or water). 

Instead of HC1 you added more [H2P04 ] to your mixture. What would you expect the red and blue litmus test to show Explain. 

The fogging of the breath, litmus test, and smoking with ammonia indicate that hydrogen bromide is freely evolved. The reddish tinge to the gas and the coloring of iodide-starch paper indicate the presence of a rather small amount of free bromine. 

The neutral salt of a base as strong as ammonium hydroxide is practically not hydrolyzed at all in cold water, certainly not enough to show by the litmus test. Water at 100° is ionized about ten times as much as at ordinary temperature and consequently the hydrolysis of the ammonium sulphate is increased ... 

Place a few drops of the neutral (litmus) test solution upon potassium hexa-cyanocobaltate(III) (or cobalticyanide, Rinmann s green) test paper. Dry the paper over a flame and ignite in a small crucible. Observe the colour of the ash against a white background part of it will be green. 

Perhaps another litmus test of the ability of the alkynic C—H group to donate a proton in a H-bond arises when a molecule of this type is paired with a hydrogen halide, HX. One then has two distinct possibilities. The X atom, although a weak proton acceptor by nature, can form a complex of the C—H—XH type. An alternative would have the XH acting as the proton donor, with the electron-rich alkyne triple bond acting as the acceptor. Experimental measurements indicate the latter is the more stable of the two alternatives. Indeed, a similar sort of geometry is adopted when HE approaches the n system of ethylene , even though the electron source in this double bond is less rich than in the triple bond of an alkyne. 

Testing the Nature of Substances.—The presence or absence of an acid or base may be found by the litmus test, but such a test reveals only the properties of the substance examined. Other tests must be made to determine whether or not a particular substance is an acid, base, or salt. 

Experiment 51. — Determine by the litmus test the nature of lemon juice, vinegar, soap, sweet and sour milk, washing soda, borax, wood ashes, faucet water, baking soda, sugar, cream of tartar, the juice of any ripe fruit and any green fruit. 

Invert a bottle, and hold its mouth beneath the water in a pneur matic trough. Describe the result. What property of the gas does this result illustrate How would a rise of temperature affect the result Compare this property with that of oxygen, hydrogen, nitrogen, and air under similar conditions. Apply the litmus test to the liquid in the bottle, or to the liquid beneath the mouth of the bottle. 

J. C. Wharton, A New Litmus Test Paper, Confederate States Medical and Surgical Journal 1 (1864) 54-55. 

The litmus test for metis is practical success. Did the navigator make the trip safely Did Odysseus s stratagems outwit the Cyclops Did the poultice cure the boil Was the farmer s harvest abundant If a technique works effectively and repeatedly for the purpose intended, the... 

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