The daily morning journal and courier., 1899-12-28

rected and unmoditied results of eX
 pertinent. But he also stated his opin
 ion as to the degree in which his re-
 suits approXimated, not to the mean of
 a larger number of experiments of the
 same kind, but to the unknown anC | unattainable true value. He expressed
 the hope that his value would be found | not more than one part in two hundred
 from the result of those subsequent ex-
 periments which should be thought sat
 is factory; and it is by just one part
 in two hundred that his value differs
 from that which is now accepted
 So the concordance of Dumas eXper-
 iments did not prove that his result wa:
 right neither did the agreement of eX- perlments by different observers. Erd- mann and Marchand made eight exper- iments by a method like that of Dumas, l with some notifications. Their result
 was 1597S, with probable error of 0.011. This value differs from that of Dumas by less than the sum of the | probable errors, so that that agreement
 is perfectly satisfactory. So, also, Regnault determined the ratio of the
 densitles of oxygen and hydrogen, from | which was computed the atomic weight
 of oxygen as 15.963, with probable er- TOT of 0.004. The results of Dumas, of Erdman and Marchand, and of Reg
 nault show very good agreement.
 But all of them. and the mean of all of
 them, we now know to be in error by one part in two hundred.
 I adduce this example. somewhat in i detail, to enforce the proposition that 1 wa ct l looking for error because observations | agree. We have experiments which l give the atomic weight of oxygen with
 a probable error of one part in fifty
 thousand, but do we know it within one part in one thousand? Each indi- vidual experimenter whose work
 would now be regarded as free from | known and tangible errors, agrees | fairly well with the mean of all For l instance, Moves results show that de-
 gree of concordance which would iusti- | fy us in expecting that, if he were to
 make hundred or thousand experi-
 ments, his final mean would be as like | ly as not to be larger or smaller by one part in nine thousand five hum dred, and his result differs from that which we accept by one part in nine hundred So Cooke and Richards as sign a value which is just as likely as not to be within one part in eight thou sand of the result which they would have obtained by multiplying observa-
 tions; and it differs from that which we
 accept by one part in fifteen hundred. But de we know that their means and
 the means of all published results tsly ;,, hxrF
 part in nine hundred? The concord ance of the results of a single experi- menter, and the agreement of different
 eXperimenters, does not justify us in asserting that we do.
 In determining the atomic weight of
 oxygen. it has been somewhat diffi- cult to determine directly all three of the quantities involved, and so to make
 what Stas called a complete synthesis, Berzelius Dumas and Erdman and
 Marchand weighed oxygen and wei he'd water, thus determining hydrogen. by difference. More recently, Dittmar and Henderson and Leduc used the same method, Cooke and Richards and kei- ser weighed hydrogen and weighed wa ter, while Rayleigh and Moves weighed hydrogen and weighed oxygen Any proceeding which weighs hydrogen di- reetly has a great advantage in preci- son different determinations in a giv- en series agree better among thein- selves, and the series of different ex- perimenters also agree better, But there is also a second, more important advantage. We have reason to believe that the constant errors involved in ,i,ao b1yJ ,al1 f1Y is possible to obtain hydrogen with less than a -thousandth or even a twen- y-thousandth of it's weight of impuri ty There is no difficulty in weighing oxygen or water with accuracy, is if we weigh hydrogen and also weigh eth- CT oxygen or water, we may hope for near approximation to the true value of the ratio sought,
 We may hope, but we cannot know. We may believe that our hydrogen is pure. and that there was no error through leakage But an unsafe stop cock might make the apparent weight of the hydrogen in a series of experi- ments seem always smaller than the fact and might yet leave the individual experiments so concordant with each other as to seem trustworthy.
 If, however, we can weigh hydrogen | and weigh oxygen, and then combine them and weigh the water produced, We f can at least give better reason for our hope, if we find that the product is nearly equal to the sum of the compo- rents The manipulation in this case is costly and is so difficult, and involves so many minute details, that not many have patience and time sufficient for it; so that no great number of such complete syntheses has been made and these few were made in conditions but little varied. When such complete ' syntheses shall have been made by diff ferent observers, with those variations of apparatus and method which may seem wise to them, we shall be able to judge of the magnitude of the errors to be feared, If such results are not con- cordant we shall have much to learn as to sources of error; but we now see some reason to expect that they will not be discordant. However. even if they are not discordant we are not to excuse ourselves from further study of of error.
 Before repeating determinations so and before studying un- known sources of errors not yet detect ed, the experimenter should receive all possible assistance from chemical the ,ry and from criticism. To boys, that