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<title>Protective colloid</title>
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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Protective colloid</span></span>
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<p>A <b>protective colloid</b> is a <a href="https://en.wiktionary.org/wiki/lyophilic" class="extiw external" title="wiktionary:lyophilic">lyophilic</a> <a href="Colloid" title="Colloid">colloid</a> that when present in small quantities keeps <a href="https://en.wiktionary.org/wiki/lyophobic" class="extiw external" title="wiktionary:lyophobic">lyophobic</a> colloids from precipitating under the <a href="Coagulation" title="Coagulation">coagulating</a> action of <a href="Electrolyte" title="Electrolyte">electrolytes</a>.
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<div class="mw-heading mw-heading2"><h2 id="Need_for_protective_colloids">Need for protective colloids</h2></div>
<p>When a small amount of <a href="Hydrophilic" class="mw-redirect" title="Hydrophilic">hydrophilic</a> colloid is added to <a href="Hydrophobic" class="mw-redirect" title="Hydrophobic">hydrophobic</a> colloids it may coagulate the latter. This is due to neutralisation of the charge on the hydrophobic colloidal particles. However, the addition of large amount of hydrophilic colloid increases the stability of the hydrophobic colloidal system. This is due to <a href="Adsorption" title="Adsorption">adsorption</a>.
</p><p>When lyophilic <a href="Sol_(colloid)" title="Sol (colloid)">sols</a> are added to lyophobic sols, depending on their sizes, either lyophobic sol is adsorbed in the surface of lyophilic sol or lyophilic sol is adsorbed on the surface of lyophobic sol. The layer of the protective colloid prevents direct collision between the hydrophobic colloidal particles and thus prevents coagulation.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>
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<div class="mw-heading mw-heading2"><h2 id="Examples">Examples</h2></div>
<p>Lyophilic sols like <a href="Starch" title="Starch">starch</a> and <a href="Gelatin" title="Gelatin">gelatin</a> act as protective colloids.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>
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<div class="mw-heading mw-heading2"><h2 id="Measurement_of_protective_action">Measurement of protective action</h2></div>
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</style><div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Gold_number" title="Gold number">Gold number</a></div>
<p>For a comparative study <a href="Richard_Adolf_Zsigmondy" title="Richard Adolf Zsigmondy">Zsigmondy</a> introduced a scale of protective
action for different protective colloids in terms of <a href="Gold_number" title="Gold number">gold number</a>. The gold number is the weight in milligrams of a protective colloid which checks the <a href="Coagulation" title="Coagulation">coagulation</a> of 10ml of a given gold sol on adding 1 ml of 10% sodium chloride.
</p><p>Thus smaller the gold number, greater is the protective action.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup>
Gold numbers of some materials
Gelatin 0.005-0.01
Albumin 0.1
Acacia 0.1-0.2
Sodium oleate 1-5
Tragacanth 2 [4]
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<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>
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<li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">
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</style><cite id="CITEREFHadkar2007" class="citation book cs1">Hadkar (2007). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=V3VIaBDTpJ8C"><i>Physical pharmacy</i></a>. p.&nbsp;96. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a>&nbsp;<bdi>978-8185790343</bdi>.</cite></span>
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<li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><cite id="CITEREFDavis1957" class="citation journal cs1">Davis, P. (1957-01-01). "Protective colloid action of gelatin". <i>Transactions of the Faraday Society</i>. <b>53</b>: <span class="nowrap">1390–</span>1394. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1039%2FTF9575301390">10.1039/TF9575301390</a>. <a href="ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a>&nbsp;<a rel="nofollow" class="external text" href="https://search.worldcat.org/issn/0014-7672">0014-7672</a>.</cite></span>
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<li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><cite id="CITEREFMurthy2008" class="citation book cs1">Murthy, Parameshwara (2008). <i>University Chemistry, Volume 2</i>. New Age International. p.&nbsp;546. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a>&nbsp;<bdi>978-8122409550</bdi>.</cite></span>
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