元明粉(fen)和(he)(he)食鹽(yan)(yan)都是強酸和(he)(he)強堿所組成的(de)鹽(yan)(yan)，易溶于水。元明粉(fen)的(de)化學名稱(cheng)是硫酸鈉(na)，食鹽(yan)(yan)化學名稱(cheng)是氯化鈉(na)。

元(yuan)明(ming)(ming)(ming)(ming)(ming)粉(fen)(fen)(fen)和(he)(he)食(shi)(shi)(shi)鹽(yan)(yan)(yan)都可(ke)(ke)(ke)用(yong)(yong)(yong)于(yu)(yu)(yu)直(zhi)接染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)、硫(liu)化染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)、還原染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)、活性(xing)染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)和(he)(he)可(ke)(ke)(ke)溶(rong)性(xing)還原染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)染(ran)(ran)(ran)(ran)(ran)棉(mian)纖(xian)維(wei)時(shi)(shi)(shi)作(zuo)(zuo)促(cu)(cu)染(ran)(ran)(ran)(ran)(ran)劑，可(ke)(ke)(ke)調節(jie)染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)對纖(xian)維(wei)的(de)(de)(de)(de)(de)上(shang)(shang)染(ran)(ran)(ran)(ran)(ran)率。元(yuan)明(ming)(ming)(ming)(ming)(ming)粉(fen)(fen)(fen)和(he)(he)食(shi)(shi)(shi)鹽(yan)(yan)(yan)也可(ke)(ke)(ke)用(yong)(yong)(yong)于(yu)(yu)(yu)酸(suan)性(xing)染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)和(he)(he)陽離(li)子(zi)染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)染(ran)(ran)(ran)(ran)(ran)羊毛和(he)(he)腈綸的(de)(de)(de)(de)(de)緩染(ran)(ran)(ran)(ran)(ran)劑，以降低纖(xian)維(wei)吸附染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)的(de)(de)(de)(de)(de)速度(du)，達到勻染(ran)(ran)(ran)(ran)(ran)的(de)(de)(de)(de)(de)要(yao)求。元(yuan)明(ming)(ming)(ming)(ming)(ming)粉(fen)(fen)(fen)和(he)(he)食(shi)(shi)(shi)鹽(yan)(yan)(yan)對染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)和(he)(he)纖(xian)維(wei)的(de)(de)(de)(de)(de)促(cu)(cu)染(ran)(ran)(ran)(ran)(ran)機理基本上(shang)(shang)是一(yi)致的(de)(de)(de)(de)(de)，由于(yu)(yu)(yu)直(zhi)接染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)等的(de)(de)(de)(de)(de)上(shang)(shang)色(se)率較低，染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)不(bu)(bu)(bu)(bu)易被纖(xian)維(wei)吸盡，染(ran)(ran)(ran)(ran)(ran)色(se)后腳水中(zhong)(zhong)殘(can)留染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)較多，加(jia)(jia)入元(yuan)明(ming)(ming)(ming)(ming)(ming)粉(fen)(fen)(fen)或(huo)食(shi)(shi)(shi)鹽(yan)(yan)(yan)后可(ke)(ke)(ke)減(jian)少(shao)染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)在水中(zhong)(zhong)的(de)(de)(de)(de)(de)溶(rong)解(jie)度(du)，促(cu)(cu)進染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)與纖(xian)維(wei)結合，增加(jia)(jia)染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)的(de)(de)(de)(de)(de)上(shang)(shang)染(ran)(ran)(ran)(ran)(ran)率。這(zhe)樣染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)的(de)(de)(de)(de)(de)用(yong)(yong)(yong)量可(ke)(ke)(ke)減(jian)少(shao)，而(er)(er)(er)染(ran)(ran)(ran)(ran)(ran)成(cheng)的(de)(de)(de)(de)(de)色(se)澤可(ke)(ke)(ke)加(jia)(jia)深(shen)。至于(yu)(yu)(yu)它們的(de)(de)(de)(de)(de)用(yong)(yong)(yong)量，取(qu)決(jue)于(yu)(yu)(yu)染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)的(de)(de)(de)(de)(de)上(shang)(shang)色(se)率及所(suo)需染(ran)(ran)(ran)(ran)(ran)成(cheng)色(se)澤的(de)(de)(de)(de)(de)深(shen)淺，不(bu)(bu)(bu)(bu)可(ke)(ke)(ke)加(jia)(jia)入太(tai)(tai)(tai)多或(huo)太(tai)(tai)(tai)快(kuai)，太(tai)(tai)(tai)多會(hui)使染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)發(fa)生(sheng)沉淀，布(bu)面造成(cheng)染(ran)(ran)(ran)(ran)(ran)斑。太(tai)(tai)(tai)快(kuai)，染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)上(shang)(shang)色(se)快(kuai)，容易產(chan)生(sheng)不(bu)(bu)(bu)(bu)勻。因此，元(yuan)明(ming)(ming)(ming)(ming)(ming)粉(fen)(fen)(fen)和(he)(he)食(shi)(shi)(shi)鹽(yan)(yan)(yan)在使用(yong)(yong)(yong)前(qian)都應用(yong)(yong)(yong)水溶(rong)化，經過濾(lv)后方可(ke)(ke)(ke)加(jia)(jia)入染(ran)(ran)(ran)(ran)(ran)浴(yu)。但要(yao)注意(yi)末染(ran)(ran)(ran)(ran)(ran)色(se)前(qian)不(bu)(bu)(bu)(bu)可(ke)(ke)(ke)加(jia)(jia)入。固染(ran)(ran)(ran)(ran)(ran)色(se)前(qian)染(ran)(ran)(ran)(ran)(ran)液濃度(du)較高，如先加(jia)(jia)入元(yuan)明(ming)(ming)(ming)(ming)(ming)粉(fen)(fen)(fen)或(huo)食(shi)(shi)(shi)鹽(yan)(yan)(yan)，染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)上(shang)(shang)染(ran)(ran)(ran)(ran)(ran)纖(xian)維(wei)過快(kuai)，容易產(chan)生(sheng)不(bu)(bu)(bu)(bu)勻染(ran)(ran)(ran)(ran)(ran)。一(yi)般都在染(ran)(ran)(ran)(ran)(ran)色(se)一(yi)段時(shi)(shi)(shi)間后，將元(yuan)明(ming)(ming)(ming)(ming)(ming)粉(fen)(fen)(fen)或(huo)食(shi)(shi)(shi)鹽(yan)(yan)(yan)加(jia)(jia)入，即中(zhong)(zhong)途加(jia)(jia)入或(huo)可(ke)(ke)(ke)幾次加(jia)(jia)入。實踐(jian)證明(ming)(ming)(ming)(ming)(ming)，用(yong)(yong)(yong)元(yuan)明(ming)(ming)(ming)(ming)(ming)粉(fen)(fen)(fen)作(zuo)(zuo)促(cu)(cu)染(ran)(ran)(ran)(ran)(ran)劑時(shi)(shi)(shi)，所(suo)染(ran)(ran)(ran)(ran)(ran)色(se)澤較鮮艷、明(ming)(ming)(ming)(ming)(ming)亮，而(er)(er)(er)用(yong)(yong)(yong)食(shi)(shi)(shi)鹽(yan)(yan)(yan)作(zuo)(zuo)促(cu)(cu)染(ran)(ran)(ran)(ran)(ran)劑時(shi)(shi)(shi)，其(qi)效果較差。這(zhe)與食(shi)(shi)(shi)鹽(yan)(yan)(yan)的(de)(de)(de)(de)(de)純凈度(du)有(you)關(guan)。因為(wei)一(yi)般工業用(yong)(yong)(yong)鹽(yan)(yan)(yan)中(zhong)(zhong)，除了含(han)有(you)較多鈣、鎂等離(li)子(zi)外，還含(han)少(shao)量鐵離(li)子(zi)，而(er)(er)(er)某(mou)些染(ran)(ran)(ran)(ran)(ran)料(liao)(liao)(liao)受鐵離(li)子(zi)的(de)(de)(de)(de)(de)影響會(hui)引起色(se)光灰暗(an)。也有(you)人(ren)認為(wei)食(shi)(shi)(shi)鹽(yan)(yan)(yan)價格便(bian)宜而(er)(er)(er)不(bu)(bu)(bu)(bu)擬采用(yong)(yong)(yong)元(yuan)明(ming)(ming)(ming)(ming)(ming)粉(fen)(fen)(fen)。實踐(jian)證明(ming)(ming)(ming)(ming)(ming)：染(ran)(ran)(ran)(ran)(ran)淺色(se)～中(zhong)(zhong)色(se)時(shi)(shi)(shi)，應以元(yuan)明(ming)(ming)(ming)(ming)(ming)粉(fen)(fen)(fen)為(wei)佳，染(ran)(ran)(ran)(ran)(ran)深(shen)色(se)則可(ke)(ke)(ke)采用(yong)(yong)(yong)食(shi)(shi)(shi)鹽(yan)(yan)(yan)。

元明粉(fen)和食(shi)鹽用于酸(suan)(suan)性(xing)(xing)染(ran)(ran)(ran)料(liao)(liao)絲(si)綢、羊毛作(zuo)緩染(ran)(ran)(ran)劑(ji)的(de)(de)(de)機理(li)是：羊毛和絲(si)綢都屬蛋質纖(xian)(xian)(xian)(xian)維。纖(xian)(xian)(xian)(xian)維分子(zi)中(zhong)含有-NH2基(ji)，當在(zai)酸(suan)(suan)性(xing)(xing)液中(zhong)用酸(suan)(suan)性(xing)(xing)染(ran)(ran)(ran)料(liao)(liao)染(ran)(ran)(ran)色，酸(suan)(suan)液中(zhong)的(de)(de)(de)氫離(li)(li)子(zi)H+很快(kuai)地擴(kuo)散到纖(xian)(xian)(xian)(xian)維內部與(yu)·NH2結(jie)合·NH3+，使纖(xian)(xian)(xian)(xian)維帶(dai)(dai)正電荷(he)(he)，而(er)(er)(er)酸(suan)(suan)性(xing)(xing)染(ran)(ran)(ran)料(liao)(liao)的(de)(de)(de)色素離(li)(li)子(zi)帶(dai)(dai)負(fu)電荷(he)(he)D-，由(you)于纖(xian)(xian)(xian)(xian)維與(yu)染(ran)(ran)(ran)料(liao)(liao)所帶(dai)(dai)電荷(he)(he)不(bu)同，而(er)(er)(er)產生離(li)(li)子(zi)鍵(jian)結(jie)合成·NH3·D。當染(ran)(ran)(ran)液中(zhong)加入元明粉(fen)或食(shi)鹽后，由(you)于元明粉(fen)帶(dai)(dai)負(fu)電荷(he)(he)的(de)(de)(de)硫酸(suan)(suan)根(gen)離(li)(li)子(zi)SO42-與(yu)食(shi)鹽帶(dai)(dai)負(fu)電荷(he)(he)的(de)(de)(de)氫離(li)(li)子(zi)能(neng)與(yu)染(ran)(ran)(ran)料(liao)(liao)的(de)(de)(de)色素離(li)(li)子(zi)D-產生競染(ran)(ran)(ran)而(er)(er)(er)優先(xian)上染(ran)(ran)(ran)纖(xian)(xian)(xian)(xian)維中(zhong)-NH3+根(gen)的(de)(de)(de)位置(zhi)，與(yu)之結(jie)合成·NH3CI或(·NH3)2SO4，而(er)(er)(er)在(zai)高溫(wen)時(shi)，D-取代了SO42-產或CI-的(de)(de)(de)位置(zhi)，使染(ran)(ran)(ran)料(liao)(liao)上染(ran)(ran)(ran)，從而(er)(er)(er)達到緩染(ran)(ran)(ran)作(zuo)用。

元(yuan)(yuan)明(ming)粉在(zai)印染(ran)(ran)生產中還可(ke)作(zuo)印花(hua)絲織(zhi)物(或(huo)(huo)有色絲織(zhi)物)精練時白地(di)色澤保護(hu)劑。在(zai)精練印花(hua)或(huo)(huo)染(ran)(ran)色絲織(zhi)物時，染(ran)(ran)料(liao)可(ke)能被(bei)剝落，以致沾污(wu)地(di)色或(huo)(huo)其(qi)它同練織(zhi)物，加入(ru)元(yuan)(yuan)明(ming)粉可(ke)減少染(ran)(ran)料(liao)的溶解度，因而不致于發生染(ran)(ran)料(liao)剝落而沾污(wu)地(di)色。食(shi)(shi)(shi)鹽(yan)還可(ke)作(zuo)納夫妥(tuo)染(ran)(ran)料(liao)打(da)底時提高吸(xi)收量。納夫妥(tuo)染(ran)(ran)棉紗時在(zai)打(da)底浴中加入(ru)一定量食(shi)(shi)(shi)鹽(yan)，可(ke)大大提高AS類色酚的吸(xi)收量，用食(shi)(shi)(shi)鹽(yan)還可(ke)作(zuo)磺化(hua)媒(mei)或(huo)(huo)鈉型陽離子，交換樹脂中作(zuo)活化(hua)劑及(ji)胰酶(mei)的活化(hua)劑。用元(yuan)(yuan)明(ming)粉則(ze)無(wu)此效果。

至于(yu)用(yong)量(liang)上的(de)區別，其兩者(zhe)的(de)關系為(wei)(wei)：5份食鹽=6份無水(shui)元明(ming)粉(fen)=12份結晶(jing)元明(ming)粉(fen)。100份無水(shui)元明(ming)粉(fen)≈100份食鹽≈227份結晶(jing)元明(ming)粉(fen)。因為(wei)(wei)結晶(jing)硫(liu)酸鈉(na)分(fen)子式為(wei)(wei)Na2SO4·10H2O分(fen)子量(liang)為(wei)(wei)322.2，而(er)無水(shui)硫(liu)酸鈉(na)分(fen)子式為(wei)(wei)Na2SO4分(fen)子量(liang)為(wei)(wei)142.06，即(ji)無水(shui)硫(liu)酸鈉(na)為(wei)(wei)結晶(jing)硫(liu)酸鈉(na)的(de)2.27倍。因此，無水(shui)元明(ming)粉(fen)和食鹽的(de)用(yong)量(liang)基本相同。