"A sadder hue then the powder of Venice glass"

Sorry about the nonexistent blogging lately; I have been slightly more active on tumblr, but a combination of post-thesis work and lassitude and the thought of a few substantive posts I've been putting off writing have combined to keep things very quiet. (A rule of thumb is that quotes offered w/o comment go there unless they are about Coleridge's drug use.) This is not a substantive post, just a few snippets of early modern science. First, I stumbled upon a piece on the "solar microscope" ca. 1816; the list it ends with is particularly worthwhile if one likes lists:

Another good bit (apart from the food-related one) is on the breeding habits of lice:

And the crystallization of salts reminded me of the bit in Browne's Pseudodoxia Epidemica on whether all crystals are forms of ice. I am not sure anyone will find this bit as charming as I did, but it is of lexicographical interest ("the stillicidous dependencies of ice"!), and then solidity-the-concept is one of my very oldest obsessions (I even wrote a dreadful term paper my freshman year on Locke and solidity...):

Pliny is positive in this Opinion: Crystallus fit gelu vehementius concreto: [...] Neither doth there any thing properly conglaciate but water, or watery humidity; for the determination of quick-silver is properly fixation, that of milk coagulation, and that of oyl and unctuous bodies, only incrassation [...]

[...] Ice although it seemeth as transparent and compact as Crystal, yet is it short in either; for its atoms are not concreted into continuity, which doth diminish its translucency; it is also full of spumes and bubbles, which may abate its gravity. And therefore waters frozen in Pans, and open Glasses, after their dissolution do commonly leave a froth and spume upon them, which are caused by the airy parts diffused in the congealable mixture which uniting themselves and finding no passage at the surface, do elevate the mass, and make the liquor take up a greater place then before: as may be observed in Glasses filled with water, which being frozen, will seem to swell above the brim.

[...] As for colour, although Crystal in his pellucid body seems to have none at all, yet in its reduction into powder, it hath a vail and shadow of blew; and in its courser pieces, is of a sadder hue then the powder of Venice glass; and this complexion it will maintain although it long endure the fire. [...]

that continuity of parts is the cause of perspicuity, it is made perspicuous by two ways of experiment. That is, either in effecting transparency in those bodies which were not so before, or at least far short of the additional degree: So Snow becomes transparent upon liquation, so Horns and Bodies resolvable into continued parts or gelly. The like is observable in oyled paper, wherein the interstitial divisions being continuated by the accession of oyl, it becometh more transparent, and admits the visible rayes with less umbrosity. Or else the same is effected by rendering those bodies opacous, which were before pellucid and perspicuous.

So Glass which was before diaphanous, being by powder reduced into multiplicity of superficies, becomes an opacous body, and will not transmit the light. So it is in Crystal powdered, and so it is also before; for if it be made hot in a crucible, and presently projected upon water, it will grow dim, and abate its diaphanity; for the water entering the body, begets a division of parts, and a termination of Atoms united before unto continuity.

The ground of this Opinion might be, first the conclusions of some men from experience; for as much as Crystal is found sometimes in rocks, and in some places not much unlike the stirrious^[14] or stillicidious dependencies of Ice. Which notwithstanding may happen either in places which have been forsaken or left bare by the earth, or may be petrifications, or Mineral indurations, like other gemms, proceeding from percolations of the earth disposed unto such concretions.

The fine structure of stains

I blogged last year about the Chicago group's work on why coffee-stains are ring-shaped, with a sharp outer edge fading as one moves in. A quick reminder:

(In other words, the edge of a droplet is stuck where it is; as the droplet evaporates, more and more of the water must move from the center to the edge, so that most of the water gets to the edge before it evaporates, so most of the evaporation and hence the deposition happens at the edge.)

There's a nice new article in PRL today (ungated) that takes a much closer look at the structure of a stain:

(c) is a blow-up [optical microscope] of the red square in (b) and (d) is a blow-up [electron microscope] of the red square in (c). The solute particles at the outermost edge of the stain are arranged in precise crystalline patterns; as you move further in towards the (relatively sparse) middle of the stain, the particles become randomly distributed. The physics of this turns out to be fairly simple, given what's already known about evaporation. To quote the paper:

The [solute] particle velocity increases dramatically in the last moments of the droplet’s life. We refer to this sudden change in speed as ‘‘rush hour.’’ The particles that arrive early, at a low deposition speed, form an ordered (square or hexagonal) structure. In contrast, particles that arrive during rush hour have a high speed and form a jammed, disordered phase.

[NB you could ask why there's a tendency for things to crystallize at all. In this case I think that's just electrostatic repulsion -- particles would like to be as far from each other as possible, i.e. in a crystal, but might not have any way to get there.] The authors also claim to have a theory of why one sees both hexagonal and square crystals in the ordered region [see part (d)] but I don't have the time right now to follow up that paper trail.

Update Here is the Physics blurb about this.