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Ancient civilizations had large scales, and also had much smaller scales that used a grain of wheat as the mass of known weight, which is the origin of the measure 1 grain which equals 0.0648 grams

ACCURACY OF A GRAIN OF WHEAT

The scale used by alchemist Geber (Jābir ibn Hayyān) (721 – 815), like the pre-Islamic scale Geber copied from, used a grain of wheat (which has a weight of 0.0648 grams) as the standard mass of known weight. Therefore, Geber’s scale could weigh with an accuracy of 0.0648 grams (the weight of one grain of wheat).

Someone writing at http://www.muslimheritage.com/chemistry badly botches the explanation of this fact, instead writing that Jābir ibn Hayyān “built a precise scale that weighed items 6,480 times smaller than the kilogram (anticipating Dalton by ten centuries)”.

This claim has several errors, and the mention of Dalton is dishonesty bordering on being an outright lie.

First of all, the claim implies that the lightest object that can be weighed is 1/ 6480 of a kilogram. That does not match the weight of 1 grain of wheat, 2 grains of wheat, or 3 grains of wheat, but somewhere between 2 grains and 3 grains. It is a weird statement to make.

It was probably intended to mean that the accuracy of the scale was plus or minus the weight of one grain of wheat, but he did the math wrong and came up with the wrong number.

The only way I can imagine how that result was obtained was to confuse the number of grains per gram with the number of grams per grain, That would give the number 64.8 grains of wheat weighs a kilogram. Since that was obviously wrong, he probably mistakenly assumed he had put the decimal point in the wrong place, so he multiplied 64.8 by 100 to obtain the number 6480.

Then, by mentioning Dalton, he falsely implies the scale could measure with nearly the accuracy of plus or minus a dalton (approximately the weight of one proton or neutron).

Actually, a kilogram is not roughly 6480 daltons but approximately 602,000,000,000,000,000,000,000,000 daltons.

[muslimheritage.com has ties to the organization that created the “1001 Inventions” traveling show, which makes hundreds of false statements.]

The articles at muslimheritage.com vary in quality. For example, the article about telescopes after the end of the Islamic Golden Age but before modern times is excellent.

Muslims a few centuries later, using a similar scale, published a list of how heavy various solids and liquids were, compared to water. Half of their results were accurate to within plus or minus two percent of modern known values.

HYDROSTATIC SCALE

Muslims did invent a scale useful for determining whether something was actually made of gold, but the alchemist Geber played no part in its invention.

Al-Biruni (973-1048) and several earlier Muslims devised scales that measured the weight of an object while it was submerged in water, and compared this to its weight when not submerged in water. From this they could calculate its specific gravity (how heavy it was compared to the weight of an equal volume of water). This gave more accurate results than the Archimedes method of measuring the amount of water displaced when the object was dropped into a container full of water.

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