Sep 062017

Today is the birthday (1766) of John Dalton FRS, English chemist, physicist, and meteorologist, best known (by people who know about these things) for proposing the basis of modern atomic theory. Dalton was born into a Quaker family in Eaglesfield, near Cockermouth, in the Lake District. His father was a weaver. He received his early education from his father and from Quaker John Fletcher, who ran a private school in the nearby village of Pardshaw Hall. Dalton’s family did not have enough money to support him in school for long, so he began to earn his living at the age of 10 in the service of a wealthy local Quaker, Elihu Robinson. It is said he began teaching at a local school at age 12, and became proficient in Latin at age 14.

When he was 15, Dalton joined his older brother Jonathan in running a Quaker school in Kendal, about 45 miles (72 km) from his home. Around the age of 23, Dalton may have considered studying law or medicine, but his relatives did not encourage him, perhaps because being a Dissenter, he was barred from attending English universities. He acquired most of his scientific knowledge from informal instruction by John Gough, a blind natural philosopher. At the age of 27 he was appointed teacher of mathematics and natural philosophy at the “New College” in Manchester, a dissenting academy. He remained there until the age of 34, when the college’s worsening financial situation led him to resign his post and take up a new career as a private tutor in mathematics and natural philosophy.

Dalton’s early life was strongly influenced by Elihu Robinson, who was a competent meteorologist and instrument maker, and who interested him in problems of mathematics and meteorology. In 1787 at age 21 he began his meteorological diary in which, during the succeeding 57 years, he entered more than 200,000 observations. He rediscovered George Hadley’s theory of global atmospheric circulation (now known as the Hadley cell) around this time. In 1793 Dalton’s first publication, Meteorological Observations and Essays, contained the seeds of several of his later discoveries but despite the originality of his treatment, little attention was paid to them by other scholars. His Elements of English Grammar, was published in 1801.

After leaving the Lake District, Dalton returned annually to spend his holidays studying meteorology and climbing mountains to measure their height. He took measurements of temperature and humidity at various altitudes which he estimated using a barometer. Until the Ordnance Survey published maps for the Lake District in the 1860s, Dalton was one of the few sources of information on altitudes in the region.

In 1794, shortly after his arrival in Manchester, Dalton was elected a member of the Manchester Literary and Philosophical Society, the “Lit & Phil”, and a few weeks later he communicated his first paper on “Extraordinary facts relating to the vision of colours”, in which he postulated that inability in color perception was caused by discoloration of the liquid medium of the eyeball. Both he and his brother were color blind, and so postulated (correctly) that the condition must be hereditary. He was able to recognize only blue, purple, and yellow. At the time (and still to an extent today), being colorblind was a severe handicap to being an analytic chemist.

The most important of all Dalton’s investigations concern atomic theory in chemistry. How he came up with the theory is not fully understood. The theory may have been suggested to him either by researches on ethylene (olefiant gas) and methane (carburetted hydrogen) or by analysis of nitrous oxide (protoxide of azote) and nitrogen dioxide (deutoxide of azote). These investigations may have led him to the idea that chemical combination (the production of definable compounds) consists in the interaction of atoms of definite and characteristic weight. Or the idea of atoms may have arisen in his mind as a purely physical concept, forced on him by study of the physical properties of the atmosphere and other gases. The first published indications of this idea are to be found at the end of his paper “On the Absorption of Gases by Water and other Liquids” where he says:

Why does not water admit its bulk of every kind of gas alike? This question I have duly considered, and though I am not able to satisfy myself completely I am nearly persuaded that the circumstance depends on the weight and number of the ultimate particles of the several gases. This is the germ of the idea that elements are composed of atoms and that the atoms of different elements have different weights.

The main points of Dalton’s atomic theory are:

Elements are made of extremely small particles called atoms.

 Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.

 Atoms cannot be subdivided, created, or destroyed.

 Atoms of different elements combine in simple whole-number ratios to form chemical compounds.

Dalton published his table of relative atomic weights containing six elements, hydrogen, oxygen, nitrogen, carbon, sulfur, and phosphorus, with the atom of hydrogen conventionally assumed to weigh 1. He provided no indication in this paper how he had arrived at these numbers but in his laboratory notebook, dated 6 September 1803, is a list in which he set out the relative weights of the atoms of a number of elements, derived from analysis of water, ammonia, carbon dioxide, etc. by chemists of the time.

Compounds were listed as binary, ternary, quaternary, etc. (molecules composed of two, three, four, etc. atoms) in the New System of Chemical Philosophy depending on the number of atoms a compound had in its simplest, empirical form. Dalton hypothesized the structure of compounds can be represented in whole number ratios. So, one atom of element X combining with one atom of element Y is a binary compound; one atom of element X combining with two elements of Y is a ternary compound, and so on. Many of the first compounds listed in the New System of Chemical Philosophy correspond to modern views, although many others do not.

Dalton used his own symbols to visually represent the atomic structure of compounds (see above). They were depicted in the New System of Chemical Philosophy, where he listed 20 elements and 17 simple molecules.

He always objected to the chemical notation devised by Jöns Jakob Berzelius (the one using letters for elements that we use today), although most thought that it was much simpler and more convenient than his own cumbersome system of circular symbols.

Dalton never married and had only a few close friends. As a Quaker, he lived a modest and unassuming personal life. For the 26 years prior to his death, Dalton lived in a room in the home of the Rev W. Johns, a published botanist, and his wife, in George Street, Manchester. Dalton and Johns died in the same year (1844).

Dalton’s daily round of laboratory work and tutoring in Manchester was broken only by annual excursions to the Lake District and occasional visits to London. In 1822 he paid a short visit to Paris, and attended several of the earlier meetings of the British Association at York, Oxford, Dublin and Bristol.

Dalton suffered a minor stroke in 1837, and a second in 1838 left him with a speech impairment, although he remained able to perform experiments. In May 1844 he had another stroke. On 26th July 1844 he recorded with trembling hand his last meteorological observation. On 27th July 1844, in Manchester, Dalton fell from his bed and was found lifeless by his attendant. He was accorded a civic funeral with full honors. His body lay in state in Manchester Town Hall for four days and more than 40,000 people filed past his coffin. The funeral procession included representatives of the city’s major civic, commercial, and scientific bodies. He was buried in Manchester in Ardwick cemetery which was later converted to a playing field, and all the graves moved.

Dalton was a native of Cumbria but he spent all of his working life as a scientist in Manchester so a Manchester recipe is suitable to celebrate his birthday.  Manchester tart is a perennial favorite that used to be a mainstay of school lunches. It’s a rich mixture of raspberries, raspberry jam, and egg custard baked in a tart shell. Some people add sliced bananas as well.

Manchester Tart


butter, for greasing
500g shortcrust pastry
plain flour, for dusting
200g raspberry jam
3 tbsp plain desiccated coconut
3 tbsp desiccated coconut, toasted in a dry frying pan until golden-brown
300g fresh raspberries
500ml milk
1 vanilla pod, split, seeds scraped out with a knife
5 egg yolks
125g caster sugar
1 tbsp cornflour
2 tbsp icing sugar, for dusting
400ml double cream, whipped until soft peaks form when the whisk is removed


Preheat the oven to 200˚C.

Grease a 24 cm tart tin with butter. Roll out the shortcrust pastry on to a lightly floured work surface to a 0.5cm thickness. Line the prepared tart tin with the pastry. Prick the pastry several times with a fork, then chill in the refrigerator for 30 minutes.

Place a sheet of baking parchment into the chilled pastry case and half-fill with dried beans. Transfer the pastry case to the oven and bake for 15 minutes, or until pale golden-brown. Remove the beans and baking parchment and return the pastry case to the oven for a further 4-5 minutes, or until pale golden-brown.

Spread the raspberry jam over the pastry base in an even layer. Sprinkle over the three tablespoons of non-toasted desiccated coconut and half of the fresh raspberries. Set the pastry base aside.

Bring the milk, vanilla pod and vanilla seeds to the boil in a pan, then reduce the heat to a simmer and simmer for 1-2 minutes. Remove the vanilla pod.

In a bowl, beat together the egg yolks and sugar until well combined. Pour the hot milk and vanilla mixture over the egg and sugar mixture, whisking continuously, until the mixture is smooth and well combined. Return the mixture to the pan over a medium heat. Whisk in the cornflour, gradually until well combined, then heat, stirring continuously until the mixture is thick enough to coat the back of a spoon. Transfer the custard mixture to a clean bowl and dust with the icing sugar to prevent a skin forming on the surface of the custard. Set aside to cool, then chill in the refrigerator for 30 minutes.

Fold the whipped double cream into the chilled custard mixture until well combined. Spoon the custard and cream mixture into the pastry case in an even layer. Sprinkle over the remaining fresh raspberries.

To serve, sprinkle over the three tablespoons of toasted desiccated coconut. Serve immediately.

Jun 152017

This date in 1752 is the traditional date set for Ben Franklin’s kite flying experiment meant to prove that lightning is electricity. If he had performed the experiment as commonly thought of, and depicted, he would almost certainly have been electrocuted.  He was much more cautious, however, and it’s worth discussing Franklin and electricity on this date because what he discovered led to new directions for science. First, I will admit that I have already discussed this topic briefly here:  This is what I said:

According to the canonical tale, Franklin realized the dangers of using conductive rods and instead used a kite. According to the legend, Franklin kept the string of the kite dry at his end to insulate him while the rest of the string was allowed to get wet in the rain to provide conductivity. A house key was attached to the string and connected to a Leyden jar (a primitive capacitor), which Franklin assumed would accumulate electricity from the lightning. The kite wasn’t struck by visible lightning (had it done so, Franklin would almost certainly have been killed) but Franklin did notice that the strings of the kite were repelling each other and deduced that the Leyden jar was being charged. Franklin reportedly received a mild shock by moving his hand near the key afterwards, because as he had estimated, lightning had negatively charged the key and the Leyden jar, proving the electric nature of lightning.

Fearing that the test would fail, or that he would be ridiculed, Franklin took only his son to witness the experiment, and then published the accounts of the test in third person. The standard account of Franklin’s experiment was disputed following an investigation and experiments based on contemporaneous records by science historian Tom Tucker, the results of which were published in 2003. According to Tucker, Franklin never performed the experiment, and the kite as described is incapable of performing its alleged role. Further doubt about the standard account has been cast by an investigation by the television series MythBusters. The team found evidence that Franklin would have received a fatal current through his heart had the event actually occurred. Nevertheless, they confirmed that certain aspects of the experiment were feasible – specifically, the ability of a kite with sufficiently damp string to receive and send to the ground the electrical energy delivered by a lightning strike.

Now let’s look deeper.

Franklin started exploring the phenomenon of electricity in 1746 when he saw some of Archibald Spencer’s lectures using static electricity for illustrations. Franklin proposed that “vitreous” and “resinous” electricity were not different types of “electrical fluid” (as electricity was called then), but the same “fluid” under different pressures. He was the first to label them as positive and negative respectively, and he was the first to discover the principle of conservation of charge. In 1748 he constructed a multiple plate capacitor, that he called an “electrical battery” (not to be confused with Volta’s pile) by placing eleven panes of glass sandwiched between lead plates, suspended with silk cords and connected by wires.

In 1750, he published a proposal for an experiment to prove that lightning is electricity by flying a kite in a storm that appeared capable of becoming a lightning storm. On May 10, 1752, Thomas-François Dalibard of France conducted Franklin’s experiment using a 40-foot-tall (12 m) iron rod instead of a kite, and he extracted electrical sparks from a cloud. On June 15 Franklin may possibly have conducted his well-known kite experiment in Philadelphia, successfully extracting sparks from a cloud, but there is no definitive evidence for this. However we do know that Franklin did conduct kite experiments around this time, although the results were not written up (with credit to Franklin) until Joseph Priestley’s 1767 History and Present Status of Electricity. Franklin was careful to stand on an insulator, keeping dry under a roof to avoid the danger of electric shock. Prof. Georg Wilhelm Richmann replicated the experiment in Russia in the months following Franklin’s experiment and was, indeed, killed by electrocution.

In his writings, Franklin indicates that he was aware of the dangers and offered alternative ways to demonstrate that lightning was electrical, as shown by his use of the concept of electrical ground. If Franklin ever did perform the experiment he proposed he certainly did not do it in the way that is often described—flying the kite and waiting to be struck by lightning. He did however use a kite to collect some electric charge from a storm cloud to prove that lightning was electrical. On October 19 in a letter to England with directions for repeating the experiment, Franklin wrote:

When rain has wet the kite twine so that it can conduct the electric fire freely, you will find it streams out plentifully from the key at the approach of your knuckle, and with this key a phial, or Leyden jar, may be charged: and from electric fire thus obtained spirits may be kindled, and all other electric experiments [may be] performed which are usually done by the help of a rubber glass globe or tube; and therefore the sameness of the electrical matter with that of lightening completely demonstrated.

Franklin’s electrical experiments led to his invention of the lightning rod. He noted that conductors with a sharp rather than a smooth point could discharge silently, and at a far greater distance. He surmised that this could help protect buildings from lightning by attaching “upright Rods of Iron, made sharp as a Needle and gilt to prevent Rusting, and from the Foot of those Rods a Wire down the outside of the Building into the Ground; … Would not these pointed Rods probably draw the Electrical Fire silently out of a Cloud before it came nigh enough to strike, and thereby secure us from that most sudden and terrible Mischief!” Following a series of experiments on Franklin’s own house, lightning rods were installed on the Academy of Philadelphia (later the University of Pennsylvania) and the Pennsylvania State House (later Independence Hall) in 1752.

In recognition of his work with electricity, Franklin received the Royal Society’s Copley Medal in 1753, and in 1756 he became one of the few 18th-century North Americans elected as a Fellow of the Society. He received honorary degrees from Harvard and Yale universities. The cgs unit of electric charge has been named after him: one franklin (Fr) is equal to one statcoulomb.

Franklin advised Harvard University in its acquisition of new electrical laboratory apparatus after the complete loss of its original collection, in a fire which destroyed the original Harvard Hall in 1764. The collection he assembled would later become part of the Harvard Collection of Historical Scientific Instruments, now on public display in its Science Center.

According to Michael Faraday, Franklin’s experiments on the non-conduction of ice are worth mentioning, although the law of the general effect of liquefaction on electrolytes is not attributed to Franklin. However, as reported in 1836 by A. D. Bache of the University of Pennsylvania, the law of the effect of heat on the conduction of bodies that are otherwise non-conductors, for example, glass, could be attributed to Franklin. Franklin writes, “A certain quantity of heat will make some bodies good conductors, that will not otherwise conduct …And water, though naturally a good conductor, will not conduct well when frozen into ice.”

Franklin took a great deal of interest in the food products grown in Britain and North America, generally expressing a preference for the latter.  He did, however, send seeds of kale (which he called “Scotch cabbage”) and rhubarb to friends back home. I suspect he was more interested in the medicinal properties of the roots of rhubarb than the food uses of the stalks. In return he asked his wife to send him apples and cranberries which she sent by the barrel load !! He could get apples in England, of course, but he preferred American Newton pippins for roasting over the apples he could find there. Cranberries of several species are indigenous to all northern temperate regions, but they did not catch on as a domesticated species in Europe in the way that they did in North America. Even in the United States they’re hard to find uncooked these days except around Thanksgiving; most are commercially processed into juice, sauces, and jellies. If you can find plain cranberries you might consider making a tart. Here’s one idea using a custard filling and quite a lot of brown sugar to counter the sourness of the cranberries. I generally use a prepared tart shell out of laziness, but you can make your own pastry if you wish.

Cranberry Custard Tart


9” tart crust
1 ½ cups granulated sugar
¼ cup water
2 cups cranberries (10 oz)
2 large eggs
½ cup brown sugar
1 ½ tsp all-purpose flour
¼ cup light cream
½ tsp almond extract
confectioners’ sugar


Preheat the oven to 350°F/175°C.

Blind bake the tart shell by lining it with foil and filling with pie weights or dried beans. Bake the tart shell for about 30 minutes, until the rim is lightly golden. Remove the foil and weights and bake for another 5 minutes, until it is lightly golden all over. Set the tart pan on a wire rack.

Increase the oven temperature to 375°F/190°C

Meanwhile, make the filling in a medium saucepan by combining the granulated sugar with the water and cook over moderately high heat, stirring, until the sugar dissolves. Add the cranberries, cover and cook over moderate heat for 3 minutes, stirring once or twice. Remove the pan from the heat and let the cranberries cool to room temperature. Drain the cranberries well and reserve the cranberry syrup.

In a medium bowl, make a custard by beating the eggs with the brown sugar and flour. Whisk in the light cream and the almond extract. Spread the cranberries in the tart shell. Drizzle 1 tablespoon of the reserved cranberry syrup over the cranberries, then pour in the almond custard.

Bake the tart in the lower third of the oven until a skewer inserted in the center comes out clean, 16 to 18 minutes. Transfer the tart in the pan to a wire rack to cool completely, at least 2 hours. Dust with confectioners’ sugar.