HCl as gaseous flux in babbitting operations; viili and piima; buttermilk

[eub]

Browsing in the Merck Index, I am informed that HCl is used "as a gaseous flux in babbitting operations". Can't find any details on the web about how that is done. I had the idea that flux literally carried the oxide off the metal surface, which HCl gas seems like it would have a hard time doing. But maybe that's not it. Anyhow, gaseous fluxes and babbitting are just an endearing pair of technologies.

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http://www.thesoydailyclub.com/SFC/dairy48.asp

First, the term "piima" is often used generically to refer to all of the many Finnish cultured milk products. Second, viili traditionally referred to the choice, rich, creamy layer that formed on the top of a bowl of piima; the less rich, bottom portion, specifically called piima, was often served as a refreshing drink. Today, however, viili and piima are generally made separately; viili is thicker and more stretchy. Finally, there are a number of similar or slightly different cultured milk products, which have various names in different parts of Finland. For example, viili is stretchy in west and north Finland, but not in east Finland.

In viili a significant proportion of these microorganisms are slime/capsule formers; microscopic analysis shows that many of the individual organisms, composed of chains of bacteria (streptococci), form a thin jellylike capsule around them. Moreover, in viili, a surface-growing milk mold (Oospora lactis or Geotrichum candidum) is usually present; it forms a prized, velvet-like layer on the surface of the unhomogenized milk.

http://www.rwood.com/Articles/Kefir_Fil_Mjolk_and_Viili.htm

I made viili a few times but then let the culture slip into oblivion. Although its flavor was pleasurable, I didn't take to its texture which can be imagined from the following story. A friend poured a cup of viili and unintentionally filled it a drop over the brim. The ringing phone distracted him and, upon return, he found an empty cup in a thick puddle of viili. The overfull drop had oozed down the cup's side and, like a slinky, had emptied it.

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I was reminded of viili and piima by the buttermilk I grew, which has a not entirely dissimilar texture. More clabbery than I was expecting -- and tasting more like yogurt; the commercial dehydrated buttermilk I've used had more diacetyl-type scent to it. I wonder if they add that.

Comments

more than you probably wanted to know about chemistry

[meerkat299.livejournal.com]

HCl is actually rather common method of doing any type of metal plating.

Some chemistry notes:
H₂(g) and H⁺ = Hydrogen in its molecular (gaseous) and ionic forms
Cl₂(g) and Cl⁻ = Chlorine in its molecular (gaseous) and ionic forms
Zn(s) and Zn²⁺ = element in its metallic (solid) and ionic forms; in this case I am using Zinc but it can be any metal
⇔ = denotes the "equal sign" between the two sides of a chemical equation; it should really be a double arrow, but this is one limitation of the Latin-1 character set.

Also note, that when hydrochloric acid (HCl) is in water (an aqueous solution) there is no virtually no attraction between it and H⁺. The H⁺ just gets surrounded by water molecules and has little interaction with the Cl⁻. Thus, I will be writing HCl(aq) as just Cl⁻. H⁺ is sometimes written as H₃O⁺ for this same reason. This is not true for all negative ions, but, in water, it is true for chlorine and five others—these six are known as the Strong Acids.

Scenario
If you were to take a beaker of water that contains Zn²⁺ and place a copper penny into the beaker. Then add HCl(aq) (hereafter referred to as Cl⁻). The Zn will plate onto the penny and a toxic yellow gas Cl₂ will bubble out of the water.

What is happening is that, in the presence of Zn²⁺, Cl⁻ will readily give up its extra electron and pair up with another chlorine and fly away. Anything that goes from liquid to solid likes to have some sort of "seed" to anchor the process of solidifying. In this case, the penny is this seed, but it can really be any solid matter, even a microscopic bit of dust.

The actual chemical reaction is:
Zn²⁺ + 2 Cl⁻ ⇔ Zn(s) + Cl₂(g)

Other things of note (and why I chose this scenario) is that a penny that is plated in zinc looks very similar to being made of the same metal used for nickels, dimes, and quarters (a copper-nickel alloy). Additionally, over time, the zinc from the plating gradually mixes with the copper from the original penny. This mix (a.k.a. alloy) of zinc and copper is more commonly known as the yellow-gold colored metal, brass. If the plating is not too thick, this transition can also be done in less than a minute by slightly heating the penny, even by simply rubbing it between your fingers.

Re: more than you probably wanted to know about chemistry

[meerkat299.livejournal.com]

I did check my books as to the likelyhood of them talking about actually reducing the copper oxide and antimony oxide back to the non-oxidized forms, but it looks to be quite impractical compared to just plating a thin layer of antimony over the top of the oxidized metal.