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Why was Avogadro's number chosen to be the value that it is? Your question implies that you already know that it was a choice rather than something derived from first principle. There are some numbers that are derived from first principles. In math, $\pi$ and $e$ are not a choice, but can be derived from their properties. In physics, the fine structure ...


16

Please do not underestimate the scientists of 19th century. They were as creative, intelligent and perhaps more genuinely dedicated to science than the scientists of the 21st century. Spectroscopy was the tool of the trade to identify and verify that a given substance is not a mixture. The original reference which established that Didymium was a mixture is ...


13

From the practical historical perspective chemists and physicists needed a number to use as a conversion factor from Daltons to grams to perform stoichiometric reactions. In the beginning, Dalton proposed to use the mass of the Hydrogen and assign it to a value of 1 Dalton without knowing how many grams correspond to 1 Dalton. Scales use grams, not daltons ...


9

Initially the Avogadro was defined as the number of atoms contained in 1 g Hydrogen. Later on, it was understood that Hydrogen can contain various amounts of Deuterium. So that, instead of referring to the fluctuating H atom, it was decided that the Avogadro would be related to the weight of another atom. There had been long discussions about the choice of ...


8

The identification of urolithins as products of human metabolism of ellagic acid was reported by Cerda et al. in the European Journal of Nutrition in 2004. The full reference is Cerda, B., Espin, J.C., Parra, S., Martinez, P. and Tomas-Barberan, F.A. (2004) The potent in vitro antioxidant ellagitannins from pomegranate juice are metabolised into bioavailable ...


6

I am afraid you are mixing all modern and old concepts. Moles and the concept of limiting reagents did not exist in Richter's time. It took 615 parts by weight of magnesia (MgO), for example, to neutralize 1000 parts by weight of sulfuric acid This relatively famous statement has nothing to do with law of multiple proportions but it illustrates the ...


5

As @Zhe says, the name urolithin A seems to have derived from the word urolith which is basically kidney stone. Quoting from here1: The name urolithin was first given to two metabolites isolated from the renal calculus of sheep (Trifolium subterraneum has been reported as the cause of clover stone and might be a relevant source of ellagitannins) that were ...


5

It is a good question and many comprehensive works are available specifically on chemical etymologies. Many scholars have spent on portion of their life on chemical etymologies. Ignore these useless down votes or close votes. The answer essentially boils down to how money are you willing to spend? I would say, if you are really keen, go for OED. After going ...


5

OP's request: I am curious as to how it (urolithin) was discovered but cannot find the story. 3,8-Dihydroxybenzo[c]chromen-6-one or 3,8-dihydroxy-6H-dibenzo[b,d]pyran-6-one (CAS #: 1143-70-0), now known as urolithin-A is first discovered as a metabolite of ellagic acid from mice in 2003 (Ref.1) by the same research group who also discovered that in as a ...


5

According to the Oxford English Dictionary entry on "ethylene", the first English usage was in 1849 in the Chemical Gazette (alternate name Journal of Practical Chemistry), published in London. The specific citation is Vol. 7 p. 116 (Mar. 15, 1849). The sentence in which it is used is in an article by "A. Wurtz" titled "On a Series ...


5

One of the most important examples of a misidentified element is coronium. This element (or what was thought to be a new element) came to play a major role in our understanding of the Sun. Originally identified by spectroscopic analysis of the Sun's corona during a solar eclipse, coronium turned out to be iron so heavily ionized that to account for it, ...


4

Thomson described the mechanical effect produced by cathodic rays on the first edition of its book Conduction of Electricity Through Gases (1903, pp. 501–502) and again later on the second edition (1906, pp. 629-630). As you mentioned it refers to the Crookes experiment with the paddle wheel in which the electron beam collides with the mill coausing it to ...


4

Is it possible that in these times, the amount of energy would permit atoms larger than we have observed in nature or been able to create in the lab? Quite possibly, but we do not need to go back in time. In fact, the early moments after the Big Bang are the least likely time to find very heavy elements, as the primary elements produced initially are ...


3

It is interesting that the very first modern reference to urolithin and its identification is in 1963 in the article cited as Two constituents of clover stone, a type of urinary calculus found in sheep by Nittle, M. C.; Pope, G. S., in Biochemical Journal, 89(1), pg 67 is wrong even in SciFinder and in Google Scholar. If we check the journal website, there ...


3

This image is from Atomic Spectra and Atomic Structure by Gerhard Herzberg, ‎John William Tranter Spinks - 1944. It does not really have boxes (just boxes of a table), but spin +1/2 and spin -1/2 are shown as arrows. Of course, I am not claiming this is the first usage, just that in 1944 it existed.


3

You will have to consult "The Study of Change Chemistry in China, 1840-1949 By James Reardon-Anderson, 2003." Andselisk found the right information about his professorship in Tsinghua University but his spellings and my search spellings are different. Our Chinese fellows can elaborate more on it. As I mentioned in the comments, he studied from the ...


3

$$\frac{\ce{O}}{\ce{^16O}}=\frac{(.9976\times\ce{^16O})+(.0004\times\ce{^17O})+(.002\times\ce{^18O})}{\ce{^16O}}$$ $$=\frac{(.9976\times\ce{^16O})+(.0004\times(\ce{^16O}+1))+(.002\times(\ce{^16O}+2))}{\ce{^16O}}$$ $$=\frac{(\ce{^16O})+(.0004\times1)+(.002\times2)}{\ce{^16O}}$$ Essentially, it comes from collecting factors of $\ce{^16O}$.


2

Other answers have covered it adequately. But there's one other way in which Avogadro's constant is not completely arbitrary. It's an order-of-magnitude measure of the quantity of particles that can sustain sentience on an Earth-type planet. 12 grams of carbon-12 is a sample of matter that's roughly on the same scale as us humans. I'm serious here. How many ...


2

By measuring the rate of fall, Millikan was able to measure the fall of the oil droplets (which were dropped through a tiny hole in the upper electrical condenser) The rate of fall here means terminal velocity of oil, $v_\mathrm{t}.$ Oil was made to drop at constant rate so no acceleration. Drag force on oil drop is: $$F_\mathrm{d} = 6\pi r\eta v_\mathrm{t},...


2

The question is: Was there any false chemical element introduced in history of chemistry? The question is very broad, but the answers given so far are mainly based on modern time suggestions. For example, coronium was suggested as an element that 19th century scientists believed might exist in the corona of the sun, hence the name. According to Science ...


2

Back in 1933, John Drury Clark published 1 his "race track" periodic table that subsequently became famous as the cover of Life magazine in 1949: Looks like B and Al are nicely positioned. Just need to add an outer track for elements 105 - 118, element names and symbols for elements 97 - 103 and element 41 is niobium, Nb. 1 Clark, John D. (November 1933). "...


1

Well, interesting question, I would re-word your question as "How can one determine an atomic mass with high accuracy using gravimetric analysis? Precision simply implies that you repeated a measurement and it agrees very well with itself even though it may be wrong. What we desire is high precision and high accuracy. Almost all the naturally occurring ...


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